Chapter 06

LEARNINGOBJECTIVESUpon completion and review of this chapter, youshould be able to:

• Identify the wire types and materials used inautomotive wiring.

• Explain how wire size is determined by boththe American Wire Gauge (AWG) systemand the metric system.

• Explain the use of a wiring harness anddefine the different types of connectors andterminal ends.

• Define the ground, parallel data, serial data,and multiplexing paths.

• Identify common electrical parts and explaintheir operation.

• Explain the color-coding of automotivewiring.

• Explain the terms used in the language ofautomotive wiring diagrams.

• Identify the component symbols used inautomotive wiring schematics.

• Explain the purpose of a wiring diagram orschematic.

KEY TERMSCircuit NumberColor CodingComponent SymbolsConnectorsGround CableInstallation DiagramMetric Wire SizesMultiplexingPrimary WiringSchematic DiagramSolenoidSwitchesWeatherproof ConnectorsWire Gauge DiagramWire Gauge NumberWiring Harness

89

6ElectricalDiagrams and Wiring

ker88839_ch06.qxd 1/9/06 11:25 AM Page 89

90 Chapter Six

Figure 6-1. The wiring harness in this vehicle is typical of those in most late-model cars. (GM Service and Parts Operations)

INTRODUCTIONNow that we have discussed current flow, volt-age, sources, electrical loads, and series and par-allel circuits, in this chapter we start to build someautomotive circuits. To build a complete circuit,we must have conductors to carry the currentfrom the voltage source to the electrical loads.The conductors are the thousands of feet of wireand cable used in the complete electrical system.The vehicle chassis is also a conductor for theground side of the circuits, as we will see later. Wewill begin our study by looking at the wiring har-nesses, connectors, and terminals of the system.

The preceding chapters used symbols to showsome of the components in an automotive elec-trical system. After studying the basic parts ofthe system (voltage source, conductors, andloads), it is time to put them together into com-plete circuits.

In real-world cases, diagrams of much greatercomplexity are used. Technicians must be ableto identify each component by its symbol anddetermine how current travels from the powersource to ground. Technicians use electrical cir-cuit diagrams to locate and identify componentson the vehicle and trace the wiring in order tomake an accurate diagnosis of any malfunctionsin the system.

WIRING ANDHARNESSESAn automobile may contain as much as half a mileof wiring, in as many as 50 harnesses, with morethan 500 individual connections (Figure 6-1). Thiswiring must perform under very poor workingconditions. Engine heat, vibration, water, roaddirt, and oil can damage the wiring and its con-nections. If the wiring or connections break down,the circuits will fail.

To protect the many wires from damage and tokeep them from becoming a confusing tangle, theautomotive electrical system is organized intobundles of wire known as wiring harnesses thatserve various areas of the automobile. The wiresare generally wrapped with tape or plastic cover-ing, or they may be enclosed in insulated tubing.Simple harnesses are designed to connect twocomponents; complex harnesses are collectionsof simple harnesses bound together (Figure 6-2).

Main wiring harnesses are located behind theinstrument panel (Figure 6-3), in the engine com-partment (Figure 6-4 and Figure 6-5), and alongthe body floor. Branch harnesses are routed fromthe main harness to other parts of the system.Items 1, 2, and 3 in Figure 6-4 are ground con-nections. The colored insulation used on individ-ual wires makes it easier to trace them through

ker88839_ch06.qxd 1/9/06 11:25 AM Page 90

91

Figure 6-2. Wiring harnesses range from the simple to the complex. (DaimlerChrysler Corporation)

Figure 6-3. This instrument panel wiring harness has 41 different connectors. (GM Service and Parts Operations)

ker88839_ch06.qxd 1/9/06 11:25 AM Page 91

92 Chapter Six

Figure 6-4. The engine compartment wiring har-nesses. (GM Service and Parts Operations)

Figure 6-5. The engine wiring harnesses connects tothe individual engine components to the engine com-partment wiring harness. (GM Service and Parts Operations)

these harnesses, especially where sections of thewire are hidden from view.

Aloose or corroded connection, or a replacementwire that is too small for the circuit, will add extraresistance and an additional voltage drop to the cir-cuit. For example, a 10-percent extra drop in volt-age to the headlamps will cause a 30-percentvoltage loss in candlepower. The same 10-percentvoltage loss at the power windows or windshieldwiper motor can reduce, or even stop, motor opera-tion. All automotive electrical circuits, except thesecondary circuit of the ignition system (fromthe coil to the spark plugs), operate on 12 to 14 voltsand are called low-voltage systems. (Six-voltsystems on older cars and 24-volt systems on

trucks also are considered low-voltage systems.)The low-voltage wiring of a vehicle, with theexception of the battery cables, is called theprimary wiring. This usually includes all lighting,accessory, and power distribution circuits. By 2003,we will see 42-volt systems in some hybrid andmybrid applications. For more information aboutdiagnosing wiring problems, see the “TracingCircuits” section in Chapter 6 of the Shop Manual.

WIRE TYPES ANDMATERIALSMost automotive wiring consists of a conductorcovered with an insulator. Copper is the most com-mon conductor used. It has excellent conductivity,is flexible enough to be bent easily, solders readily,and is relatively inexpensive. A conductor must besurrounded with some form of protective coveringto prevent it from contacting other conductors.This covering is called insulation. High-resistanceplastic compounds have replaced the cloth or paperinsulation used on older wiring installations.

Stainless steel is used in some heavy wiring,such as battery cables and some ignition cables.Some General Motors cars use aluminum wiring inthe main body harness. Although less expensive,aluminum is also less conductive and less flexible.For these reasons, aluminum wires must be largerthan comparable copper wires and they generallyare used in the lower forward part of the vehiclewhere flexing is not a problem. Brown plastic wrap-ping indicates aluminum wiring in GM cars; copperwiring harnesses in the cars have a black wrapping.

Wire TypesAutomotive wiring or circuit conductors are usedin one of three forms, as follows:

• Solid wires (single-strand)• Stranded wires (multistrand)• Printed circuitry

Solid or single-strand wire is used where cur-rent is low and flexibility is not required. In auto-motive electrical systems, it is used insidecomponents such as alternators, motors, relays,and other devices with only a thin coat of enamelor shellac for insulation. Stranded or multistrand

ker88839_ch06.qxd 1/9/06 11:25 AM Page 92

Electrical Diagrams and Wiring 93

Figure 6-6. Automotive wiring may be solid-wire con-ductors or multistrand-wire conductors. (DaimlerChryslerCorporation)

Figure 6-7. Printed circuit boards are used in automo-tive instrument panels and elsewhere. (DaimlerChryslerCorporation)

wire is made by braiding or twisting a number ofsolid wires together into a single conductor insu-lated with a covering of colored plastic, as shownin Figure 6-6. Most automotive electrical systemwiring uses stranded wire, either as single con-ductors or grouped together in harnesses orlooms. For more information about wire types,see the section on “Copper Wiring Repair” inChapter 6 of the Shop Manual.

Printed circuitry is a thin film of copper orother conductor that has been etched or embeddedon a flat insulating plate (Figure 6-7). A complete

printed circuit consists of conductors, insulatingmaterial, and connectors for lamps and othercomponents, and is called a printed circuit (PC)board. It is used in places where space for indi-vidual wires or harnesses is limited, such asbehind instrument panels.

WIRE SIZEAutomotive electrical systems are very sensitiveto changes in resistance. This makes the selectionof properly sized wires critical whenever systemsare designed or circuits repaired. There are twoimportant factors to consider: wire gauge numberand wire length.

Wire Gauge NumberA wire gauge number is an expression of thecross-sectional area of the conductor. The mostcommon system for expressing wire size is theAmerican Wire Gauge (AWG) system. Figure 6-8is a table of AWG wire sizes commonly used inautomotive systems. Wire cross-sectional area ismeasured in circular mils; a mil is one-thousandthof an inch (0.001), and a circular mil is the area of acircle 1 mil (0.001) in diameter. A circular mil mea-surement is obtained by squaring the diameter of aconductor measured in mils. For example, a conduc-tor 1/4 inch in diameter is 0.250 inch, or 250 mils, indiameter. The circular mil cross-sectional area of thewire is 250 squared, or 62,500 circular mils.

Figure 6-8. This table lists the most common wiregauge sizes used in automotive electrical systems.(DaimlerChrysler Corporation)

ker88839_ch06.qxd 1/9/06 11:25 AM Page 93

94 Chapter Six

Figure 6-9. This figure shows the relationshipbetween current capacity and resistance as the cross-section of a conductor changes.

Correct Wire for Load Easy Current Movement

Wire Too Small; Restricted Current Movement

More Heat

E EE E

EE E

Gauge numbers are assigned to conductors ofvarious cross-sectional areas. As gauge numberincreases, area decreases and the conductorbecomes smaller (Figure 6-9). A 6-gauge conduc-tor is smaller than a 3-gauge conductor, and a12-gauge conductor is smaller than a 6-gaugeconductor. You learned in Chapter 1 that as thecross-sectional area of a conductor decreases, itsresistance increases. As resistance increases, sodoes the gauge number. Also, because the current-carrying ability of a conductor decreases as theresistance increases, a conductor with a highergauge number will carry less current than a con-ductor with a lower gauge number.

Remember that the wire gauge number refers tothe size of the conductor, not the size of the com-plete wire (conductor plus insulation). For example,it is possible to have two 16-gauge wires of differ-ent outside diameters because one has a thickerinsulation than the other. Twelve-volt automo-tive zelectrical systems generally use 14-, 16-, and18-gauge wire. Main power distribution circuitsbetween the battery and alternator, ignition switch,fuse box, headlamp switch, and larger accessoriesuse 10- and 12-gauge wire. Low-current electroniccircuits may use 20-gauge wire. Lighting other thanthe headlamps, as well as the cigarette lighter, radio,and smaller accessories, use 14-, 16-, and 18-gaugewire. Battery cables, however, generally are listedas 2-, 4-, or 6-AWG wire size.

The gauge sizes used for various circuits in anautomobile are generally based on the use of cop-per wire. A larger gauge size is required when alu-minum wiring is used, because aluminum is notas good a conductor as copper. Similarly, 6-volt

electrical systems require larger-gauge wires than12-volt systems for the same current loads. This isbecause the lower source voltage requires lowerresistance in the conductors to deliver the samecurrent. Generally, 6-volt systems use wires twosizes larger than 12-volt systems for equivalentcurrent loads. Future 42-volt systems will notrequire as large a wire diameter as the current12-volt system. Generally, a 42-volt system willuse two sizes smaller than 12-volt systems forequivalent current loads.

� Wire Size Matters

The following drawing shows how a large wireeasily conducts a high-amperage current, such asyou would find going to a starter motor. The heav-iest wires are often called cables, but their pur-pose is the same. On the other hand, a compara-tively light wire tends to restrict current flow, whichmay generate excess heat if the wire is too smallfor the job.Too much current running though a lightwire may cause the insulation to melt, leading to ashort circuit or even a fire.

Metric Wire SizesLook at a wiring diagram or a service manual formost late model vehicles, and you may see wiresizes listed in metric measurements. Metric wiresizes have become the norm in domestic auto-motive manufacturing due to the global econ-omy. For example, if you look at a wiring dia-gram for an import or late-model domesticvehicle, you will see wire sizes listed as 0.5,1.0, 1.5, 4.0, and 6.0. These numbers are thecross-sectional area of the conductor in squaremillimeters (mm2). Metric measurements arenot the same as circular-mil measurements;they are determined by calculating the cross-sectional area of the conductor with the follow-ing formula: Area = Radius2 × 3.14. A wire with

ker88839_ch06.qxd 1/9/06 11:25 AM Page 94


Figure 6-10. Wire gauge table: As wire lengthincreases, larger-gauge wire must be used to carry thesame amount of current.

a 1-mm cross-sectional area actually has a1.128-mm diameter. The following table listsAWG sizes and equivalent metric wire sizes.

AWG Size Metric Size Table

AWG Size (Gauge) Metric Size (mm2)

20 0.518 0.814 2.012 3.010 5.08 8.06 13.04 19.0

Wire LengthWire length also must be considered when design-ing electrical systems or repairing circuits. As con-ductor length increases, so does resistance. An18-gauge wire can carry a 10-ampere load for10 feet without an excessive voltage drop. However,to carry the same 10-ampere load for 15 feet, a16-gauge wire will be required. Figure 6-10 is atable showing the gauge sizes required for wires of

different lengths to carry various current loads. Wirelengths are based on circuits that are grounded to thevehicle chassis.

Special WiringAlthough most of the electrical system is made upof low-voltage primary wiring, special wiring isrequired for the battery and the spark plugs. Sincethese wires are larger in size than primary wiring,they are often called cables. Battery cables are low-resistance, low-voltage conductors. Ignition cablesare high-resistance, high-voltage conductors.

Battery CablesThe battery is connected to the rest of the elec-trical system by very large cables. Large cablesare necessary to carry the high current requiredby the starter motor. Figure 6-11 shows severalkinds of battery cables. Twelve-volt systemsgenerally use number 4 or number 6 AWG wirecables; 6-volt systems and some 12-volt dieselsystems require number 0 or number 1 AWGwire cables. Cables designed for a 6-volt systemcan be used on a 12-volt system, but the smallercable intended for a 12-volt system cannot beused on a 6-volt system without causing toomuch voltage drop.

Battery installations may have an insulatedground cable or one made of braided, uninsulatedwire. The braided cables or straps are flat insteadof round; however, they have the same resistanceand other electrical properties of a round cable ofequivalent gauge. Most battery cables are fitted atone end with a lead terminal clamp to connect tothe battery, although many import cars use aspring-clamp terminal. The lead terminal is usedto reduce corrosion when attached to the lead bat-tery post. A tinned copper terminal is attached tothe other end of the cable to connect to the startermotor or ground, as required.

Ignition CablesThe ignition cables, or spark plug cables, are oftencalled high-tension cables. They carry current at10,000 to 40,000 volts from the coil to the dis-tributor cap, and then to the spark plugs. Becauseof the high voltage, these cables must be very wellinsulated.

Years ago, all ignition cables were made with cop-per or steel wire conductors. During the past 30

ker88839_ch06.qxd 1/9/06 11:25 AM Page 95

96 Chapter Six

Figure 6-11. Assorted battery cables.

years, however, high-resistance, non-metallic cableshave replaced metallic conductor cables as originalequipment on cars and light trucks. Although metallic-conductor ignition cables are still made, they aresold for special high-performance or industrialapplications and are not recommended for highwayuse. The conductors used in high-resistance, non-metallic ignition cables are made of carbon, or oflinen or fiberglass impregnated with carbon. Thesecables evolved for the following reasons:

• High-voltage ignition pulses emit high-fre-quency electrical impulses or radio frequencyinterference (RFI) that interfere with radioand television transmission, as described inChapter 2. The principal method used to limitthis interference is the use of high-resistanceignition cables, often referred to as suppres-sion cables.

• The extra resistance in the cable decreasesthe current flow and thus reduces the burn-ing of spark plug electrodes. The higherresistance also helps take advantage of thehigh-voltage capabilities of the ignition sys-tem, as shown in Part Five of this manual.

The high-voltage current carried by ignitioncables requires that they have much thicker insu-lation than low-voltage primary wires. Ignitioncables are 7 or 8 millimeters in diameter, but theconductor in the center of the cable is only a smallcore. The rest of the cable diameter is the heavyinsulation used to contain the high voltage andprotect the core from oil, dirt, heat, and moisture.

One type of cable insulation material is knownby its trade name, Hypalon, but the type most com-monly used today is silicone rubber. Silicone isgenerally thought to provide greater high-voltage

insulation while resisting heat and moisture betterthan other materials. However, silicone insulationis softer and more pliable than other materials andthus more likely to be torn or damaged by roughhandling. Cables often have several layers of insu-lation over the conductor to provide the best insu-lating qualities with strength and flexibility.

CONNECTORS ANDTERMINALSElectrical circuits can be broken by the smallestgap between conductors. The gaps can be causedby corrosion, weathering, or mechanical breaks.One of the most common wear points in an auto-mobile electrical system is where two conductorshave been joined. Their insulation coats have beenopened and the conductive material exposed.Special connectors are used to provide strong,permanent connections and to protect these pointsfrom wear.

These simple connectors are usually calledwiring terminals. They are metal pieces thatcan be crimped or soldered onto the end of a wire.Terminals are made in many shapes and sizes forthe many different types of connections required.They can be wrapped with plastic electrical tapeor covered with special pieces of insulation. Thesimplest wire terminals join a single wire to adevice, to another single wire, or to a few otherwires (Figure 6-12). Terminals for connecting toa device often have a lug ring, a spade, or a hook,which can be bolted onto the device. Male andfemale spade terminals or bullet connectors areoften used to connect two individual wires

ker88839_ch06.qxd 1/9/06 11:25 AM Page 96


Figure 6-12. Some common single-wire terminals(connectors).

(Figure 6-13). For more information about the use of different types of connectors, see the“Connector Repair” section in Chapter 6 of theShop Manual.

Multiple Wire ConnectorsAlthough the simple wiring terminals just describedare really wire connectors, the term connector isnormally used to describe multiple-wire connectorplugs. This type of plug is used to connect wiring toswitches, as shown in Figure 6-14, or to other com-ponents. It also is used to join wiring harnesses.

Multiple-wire connectors are sometimes calledjunction blocks. On older vehicles, a junction blockwas a stationary plastic connector with terminals setinto it, in which individual wires were plugged orscrewed in place. Because of the time required toconnect this type of junction block on the assemblyline, it has been replaced by a modem version thataccepts several plugs from different harnesses(Figure 6-15).

Some multiple-connector plugs have as many as40 separate connections in a single plug. They pro-vide a compact, efficient way to connect wires for

individual circuits while still grouping themtogether in harnesses. Wiring connections can bemade quickly and accurately with multiple connec-tors, an important consideration in assembly-linemanufacturing.

Figure 6-13. Male and female bullet connectors andspade terminals are common automotive connectors.(DaimlerChrysler Corporation)

Figure 6-15. This junction block accepts individualwires on one side and connectors on the other.(DaimlerChrysler Corporation)

Figure 6-14. Multiple connectors are used to makecomplex switch connections. (DaimlerChrysler Corporation)

ker88839_ch06.qxd 1/9/06 11:25 AM 7

98 Chapter Six

Figure 6-16. Connectors have some form of lock toprevent accidental separation. Individual terminalsand wires can be removed from some connectors;other connectors are replaced as an entire assembly.(GM Service and Parts Operations)

Figure 6-17. A bulkhead connector, or disconnect, is mounted on many firewalls. Multiple-wire connectors pluginto both sides. (DaimlerChrysler Corporation)

Such connector plugs generally have hardplastic shells, with one half of the connectorcontaining the male terminals or pins, and theother half containing the female terminals orsockets. Probing the rear of the individual con-nections without separating the connector cantest circuit operation. A locking tab of some typeis used to prevent the connector halves from sep-arating. Separation or removal of the plug mayrequire the locking tab to be lifted or depressed(Figure 6-16).

Although many hard-shell connector designsallow removal of the individual wires or their ter-minals for repair, as shown in Figure 6-17, manu-facturers are now using plugs that are serviced asan assembly. If a wire or terminal is defective, theentire plug is cut from the harness. The replace-ment plug is furnished with 2 or 3 inches of wiresextending from the rear of the plug. These plugsare designed to be replaced by matching and sol-dering their wire leads to the harness.

Bulkhead ConnectorsA special multiple connector, called a bulkheadconnector or bulkhead disconnect, is used where a

ker88839_ch06.qxd 1/9/06 11:25 AM Page 98


Figure 6-18. Nissan uses this type of waterproofconnector. (Courtesy of Nissan North America, Inc.)

Figure 6-19. Half of the automotive electrical systemis the ground path through the vehicle chassis.

number of wiring circuits must pass through a bar-rier such as the firewall (Figure 6-17). The bulk-head connector is installed in the firewall and mul-tiple connectors are plugged into each side of it toconnect wires from the engine and front acces-sories to wires in the rest of the car.

Weatherproof ConnectorsSpecial weatherproof connectors are used in theengine compartment and body harnesses of late-model GM cars. This type of connector has a rubberseal on the wire ends of the terminals, with sec-ondary sealing covers on the rear of each connectorhalf. Such connectors are particularly useful in elec-tronic systems where moisture or corrosion in theconnector can cause a voltage drop. Some Japanesecarmakers use a similar design (Figure 6-18).

GROUND PATHSWe have spoken as if wiring carried all of the cur-rent in an automotive electrical system. In fact,wiring is only about half of each circuit. The otherhalf is the automobile engine, frame, and body,which provide a path for current flow. This side ofthe circuit is called the ground (Figure 6-19).Automotive electrical systems are called single-wire or ground-return systems.

The cable from one battery post or terminal isbolted to the car engine or frame. This is calledthe ground cable. The cable from the other bat-tery terminal provides current for all the car’selectrical loads. This is called the insulated, or

hot, cable. The insulated side of every circuit inthe vehicle is the wiring running from the bat-tery to the devices in the circuit. The groundside of every circuit is the vehicle chassis(Figure 6-19).

The hot battery cable is always the insulatedtype of cable described earlier. The ground cablemay be an insulated type of cable, or it may be abraided strap. On many vehicles additionalgrounding straps or cables are connected betweenthe engine block and the vehicle body or frame.The battery ground cable may be connected toeither the engine or the chassis, and the additionalground cable ensures a good, low-resistanceground path between the engine and the chassis.This is necessary for proper operation of the cir-cuits on the engine and elsewhere in the vehicle.Late-model vehicles, which rely heavily on com-puterized components, often use additionalground straps whose sole purpose is to minimizeor eliminate electromagnetic interference (EMI),as shown in Chapter 4.

The resistances in the insulated sides of all thecircuits in the vehicle will vary depending onthe number and kinds of loads and the length ofthe wiring. The resistance on the ground side ofall circuits, that is, between each load and itsground connection, must be virtually zero. Formore information about ground paths, see the“Copper Wiring Repair” section in Chapter 6 ofthe Shop Manual.

� Early Wiring Problems

Early automobiles had many problems with theirelectrical systems, usually the result of poor elec-trical insulation. For example, high-tension cable

ker88839_ch06.qxd 1/9/06 11:25 AM Page 99

100 Chapter Six

insulation, made by wrapping cotton or silkaround wire and then coating it with rubber, waseasily hardened by heat. The insulation oftenbroke off, leaving bare wire exposed.

A common problem in cars that used dry-cellbatteries was moisture penetration through thebattery’s paper insulation. Current design wouldflow to ground and the batteries would becomedischarged.

Even washing a car sometimes caused trou-ble. Water got into the distributor terminals andmade the engine hard to start. Some technicianspoured melted wax into the space between theplug wires and the distributor cap terminals.For protection from heat, moisture, oil, andgrease, wiring was often run through a metalconduit. Armored cable-insulated wire enclosedin a permanent, flexible metal wrapping was alsoused, especially in a circuit where any voltagedrop was critical.

This is an important point to remember. It may behelpful at this time to review the explanations inChapters 3 and 5 of voltage drops and current flowin various circuits from the source, through all theloads, and back to the source. Every electrical loadis attached to the chassis so that current can passthrough the ground and back to the grounded bat-tery terminal. Grounding connections must besecure for the circuit to be complete. In older carswhere plastics were rarely used, most loads had adirect connection to a metal ground. With theincreased use of various plastics, designers havehad to add a ground wire from some loads to thenearer metal ground. The ground wires in mostcircuits are black for easy recognition.

MULTIPLEXCIRCUITSThe use of multiplexing, or multiplex circuits, isbecoming a necessity in late-model automobilesbecause of the increasing number of conventionalelectrical circuits required by electronic controlsystems. Wiring harnesses used on such vehicleshave ballooned in size to 60 or more wires in asingle harness, with the use of several harnessesin a vehicle not uncommon. Simply put, thereare too many wires and too limited space inwhich to run them for convenient service. With somany wires in close proximity, they are subject to

electromagnetic interference (EMI), which youlearned about in Chapter 4. To meet the almostendless need for electrical circuitry in the grow-ing and complex design of automotive controlsystems, engineers are gradually reducing the sizeand number of wire and wiring harnesses by usinga multiplex wiring system.

The term multiplexing means different things todifferent people, but generally it is defined as ameans of sending two or more messages simulta-neously over the same channel. Different forms ofmultiplexing are used in automotive circuits. Forexample, windshield wiper circuits often use mul-tiplex circuits. The wiper and washer functions insuch circuit work though a single input circuit bymeans of different voltage levels. In this type ofapplication, data is sent in parallel form. However,the most common form of multiplexing in auto-motive applications is serial data transmission,also known as time-division multiplex. In thetime-division type of circuit, information is trans-mitted between computers through a series of dig-ital pulses in a program sequence that can be readand understood by each computer in the system.The three major approaches to a multiplex wiringsystem presently in use are as follows:

• Parallel data transmission• Serial data transmission• Optical data links

We will look at each of these types of system, andthen we will discuss the advantages of multiplex-ing over older systems of wiring.

Parallel Data TransmissionThe most common parallel data multiplexing cir-cuits use differentiated voltage levels as a means ofcontrolling components. The multiplex wiring cir-cuit used with a Type C General Motors pulsewiper-washer unit is shown in Figure 6-20. The cir-cuit diagram shows several major advantages overother types of pulse wiper circuits, as follows:

• Eliminating one terminal at the washer pumpreduces the wiring required between the wiperand control switch.

• Using a simple grounding-type control switcheliminates a separate 12-volt circuit to thefuse block.

• Eliminating a repeat park cycle when thewash cycle starts with the control switch inthe OFF position—in standard circuits, the

ker88839_ch06.qxd 1/9/06 11:25 AM Page 100


Figure 6-20. Parallel data transmission through differentiated voltage levels reduces the amount of wiringin this multiplex wiper-washer circuit. (DaimlerChrysler Corporation)

blades begin a wash cycle from the parkposition and return to park before continu-ing the cycle—simplifies operation.

An electronic timer controls the park and pulserelays. The timer consists of a capacitor, a vari-able resistor in the control switch, and electronicswitching circuitry. The variable resistor controlsthe length of time required to charge the capaci-tor. Once the capacitor reaches a certain level ofcharge, it energizes the electronic switching cir-cuit, completing the ground circuit to the pulserelay. This energizes the 12-volt circuit to themotor windings and the motor operates. Whenthe driver presses the wash button, it grounds thewasher pump ratchet relay coil circuits, starting awash cycle. The electronic timer circuitry usesa high-voltage signal for wiper operation and alow-voltage signal for the wash cycle.

A multiplex circuit that functions with paralleldata transmission is a good tool for simple circuitcontrol. However, transmitting data in parallelform is slower and more cumbersome than trans-mitting in serial form. This is important when thesignal is to be used by several different compo-nents or circuits at the same time.

Serial Data TransmissionSerial data transmission has become the most fre-quently used type of multiplex circuit in automo-tive applications. It is more versatile than paralleltransmission but also more complex. A single cir-cuit used to transmit data in both directions also iscalled a bus data link.

Sequencing voltage inputs transmitted in serialform can operate several different components, orelements within a single component. This allowseach component or element to receive input for aspecified length of time before the input is trans-mitted to another component or element. A four-element light-emitting diode (LED) display in theinstrument cluster is a typical example. By rotat-ing the applied voltage from left to right rapidlyenough, each segment of the display is illumi-nated 25 percent of the time, but the human eyecannot detect that fact. To the eye, the entire dis-play appears to be uniformly illuminated 100 per-cent of the time.

To prevent interference between the varioussignals transmitted, a multiplex system using busdata links must have a central transmitter (micro-processor) containing a special encoder. The sys-tem also requires a receiver with a correspondingdecoder at each electrical load to be controlled.The transmitter and each receiver are connected tobattery power and communicate through a two-way data link called a peripheral serial bus.Operational switches for each circuit to be con-trolled have an individual digital code or signaland are connected to the transmitter. When thetransmitter receives a control code, it determineswhich switch is calling and sends the control sig-nal to the appropriate receiver. The receiver thencarries out the command. If a driver operates theheadlamp switch, the transmitter signals theproper receiver to turn the headlights on or off,according to the switch position.

On the Chrysler application shown in Fig-ure 6-21, each module has its own microprocessor

ker88839_ch06.qxd 1/9/06 11:25 AM Page 101

102 Chapter Six

Figure 6-21. The DaimlerChrysler EVIC system is an example of a vehicle data communications networkthat allows separate computers to share data and communicate with each other through serial data trans-mission. (DaimlerChrysler Corporation)

connected to the data bus through the ChryslerCollision Detection (CCD) integrated circuit,which sends and receives data. The CCD circuitacts like a traffic control officer at a four-way inter-section. If the data bus is not in use, it allows unre-stricted transmission from a module. However, ifone module is transmitting, it blocks the transmis-sion of data from another module until the bus(intersection) is clear. If two or more modules startto transmit at the same time, or almost at the sametime, the CCD circuit assigns a priority to the mes-sages according to the identification code at thebeginning of the transmission. If the CCD circuitblocks a message, the module that originally sent itretransmits the signal until it is successful.

Receivers work in one of two ways: they oper-ate the electrical load directly, or they control arelay in the circuit to operate the load indirectly.They are not capable of making decisions on theirown, but only carry out commands from the trans-mitter. However, they can send a feedback signalinforming the transmitter that something is wrongwith the system.

Optical Data LinksA variation of the serial data transmissionapproach to multiplexing substitutes optical data

links or fiber-optic cables for the peripheral serialbus. The concept is the same, but light signals aresubstituted for voltage signals. An optical data linksystem operates with the transmitter and receiversdescribed earlier, but a light-emitting diode (LED)in the transmitter sends light signals through thefiber-optic cables to a photo diode in the receiver.The light signals are decoded by the receiver,which then performs the required control function.Primarily Toyota and other foreign manufacturershave used this form of multiplexing. Because ituses light instead of voltage to transmit signals,system operation is not affected by EMI, nor doesthe system create interference that might have anadverse influence on other electrical systems inthe vehicle.

Multiplex AdvantagesRegardless of the type of multiplex system used,such a circuit offers several advantages over con-ventional wiring circuits used in the past, as follows:

• The size and number of wires required for agiven circuit can be greatly reduced. As aresult, the complexity and size of wiring har-nesses also are reduced.

• The low-current-capacity switches used in amultiplex circuit allow the integration of

ker88839_ch06.qxd 1/9/06 11:25 AM Page 102


various touch-type switches into the overallvehicle design.

• The master computer or transmitter can beprogrammed with timing functions for con-venience features, such as locking doorsabove a given speed or unlocking them whenthe ignition is shut off.

ELECTRICALSYSTEM POLARITYWe discussed positive (+) and negative (�) elec-trical charges in Chapter 3. We learned that likecharges repel each other and unlike chargesattract each other. We also noted that the terminalsof a voltage source are identified as positive andnegative. In Chapter 2, we defined magneticpolarity in terms of the north and south poles of amagnet and observed that unlike poles of a mag-net attract each other, just as unlike charges do.Similarly, like poles repel each other.

The polarity of an electrical system refers tothe connections of the positive and negative ter-minals of the voltage source, the battery, to theinsulated and ground sides of the system. Alldomestic cars and trucks manufactured since1956 have the negative battery terminal con-nected to ground and the positive terminal con-nected to the insulated side of the system. Theseare called negative-ground systems and are saidto have positive polarity.

Before 1956, 6-volt Ford and Chrysler vehi-cles had the positive battery terminal connectedto ground and the negative terminal connectedto the insulated side of the system. These arecalled positive-ground systems and are said tohave negative polarity. Foreign manufacturersused positive-ground systems as late as 1969. Inboth kinds of systems, we say that currentleaves the hot side of the battery and returnsthrough the ground path to the grounded batteryterminal.

In your service work, it is very important torecognize system polarity negative or positiveground before working on the electrical system.Some electrical components and test equipmentare sensitive to the system polarity and must beinstalled with their connections matching those ofthe battery. Reversing polarity can damage alter-nators, cause motors to run backwards, ruin elec-tronic modules, and cause relays or solenoids tomalfunction.

COMMONELECTRICAL PARTSMany common electrical parts are used in variouscircuits in an electrical system. All circuits haveswitches of some kind to control current flow.Most circuits have some form of protective device,such as a fuse or circuit breaker, to protect againsttoo much current flow. Various kinds of solenoids,relays, and motors are used in many circuits, andwhatever their purpose, they operate in similarways wherever they are used.

Before we look at complete circuits and systemdiagrams later in this next chapter, we should learnabout some of the common devices used in manycircuits.

SwitchesSwitches are used in automobile electrical sys-tems to start, stop, or redirect current flow. Theycan be operated manually by the driver orremotely through mechanical linkage. Manualswitches, such as the ignition switch and the head-lamp switch, allow the driver to control the opera-tion of the engine and accessories. Examples areshown in Figure 6-22; the driver or the passengerscontrol a remotely operated switch indirectly. Forexample, a mechanical switch called a neutralsafety switch on automatic transmission gearselectors will not let the engine start if the auto-mobile is in gear. Switches operated by openingand closing the doors control the interior lights.For more information about switches, see the“Copper Wiring Repair” section in Chapter 6 ofthe Shop Manual.

Toggle Push-Pull Push ButtonSwitches exist in many forms but have common char-acteristics. They all depend upon physical movementfor operation. A simple switch contains one or moresets of contact points, with half of the points station-ary and the other half movable. When the switch isoperated, the movable points change position.

Switches can be designed so that the points arenormally open and switch operation closes them toallow current flow. Normally closed switches allowthe operator to open the points and stop currentflow. For example, in an automobile with a seatbeltwarning buzzer, the switch points are opened when

ker88839_ch06.qxd 1/9/06 11:25 AM Page 103

104 Chapter Six

Figure 6-23. These symbols for normally openswitches are used on electrical system diagrams.

the seatbelt is buckled; this stops current flow to thebuzzer. Figure 6-23 shows the electrical symbolsfor some simple normally open switches.

A switch may lock in the desired position, orit may be spring-loaded so that a constant pres-sure is required to keep the points out of theirnormal position. Switches with more than oneset of contact points can control more than onecircuit. For example, a windshield wiper switchmight control a low, medium, and high wiperspeed, as well as a windshield washer device(Figure 6-24).

Switches are shown in simplified form on elec-trical diagrams so that current flow through themcan easily be traced (Figure 6-25). Triangular con-tact points generally indicate a spring-loadedreturn, with circular contacts indicating a locking-position switch. A dashed line between the mov-able parts of a switch means that they are mechan-ically connected and operate in unison, as shownin Figure 6-26.

In addition to manual switches, automotiveelectrical circuits use a variety of other switch

designs. Switches may be operated by temperatureor pressure. Switches designed to sense enginecoolant temperature contain a bimetal arm thatflexes as it heats and cools, opening or closing theswitch contacts (Figure 6-26). Oil pressure andvacuum switches respond to changes in pressure.

Mercury and inertia switches are motion-detector switches, that is, they open and closecircuits automatically when their position is dis-turbed. A mercury switch uses a capsule contain-ing two electrical contacts at one end. The otherend is partially filled with mercury, which is agood conductor (Figure 6-27).

When the capsule moves a specified amountin a given direction, the mercury flows to theopposite end of the capsule and makes a circuitbetween the contacts. This type of switch oftenis used to turn on engine compartment or trunklamps. It can also be used as a rollover switch toopen an electric fuel pump or other circuit in anaccident.

An inertia switch is generally a normallyclosed switch with a calibrated amount of springpressure or friction holding the contacts together.Any sharp physical movement (a sudden changein inertia) sufficient to overcome the spring pres-sure or friction will open the contacts and breakthe circuit. This type of switch is used to open thefuel pump circuit in an impact collision. After theswitch has opened, it must be reset manually to itsnormally closed position.

Figure 6-22. Many different types of switches are used in thecomplete electrical system of a modern automobile.

ker88839_ch06.qxd 1/9/06 11:25 AM Page 104


Figure 6-25. This starting and ignition switch has twosets of contacts linked together by the dashed line.Triangular terminals in the start (ST) position indicatethat this position is spring-Ioaded and that the switchwill return to RUN when the key is released.(DaimlerChrysler Corporation)

Figure 6-24. The instrument panel switch in this two-speed windshield wiper circuit has two sets of con-tacts linked together, as shown by the broken line. The Park switch is operated by mechanical linkage fromthe wiper motor armature. (DaimlerChrysler Corporation)

Figure 6-26. A coolant temperature switch inits normally open position.

Figure 6-27. A mercury switch is activated by motion.

RelaysA relay is a switch that uses electromagnetism tophysically move the contacts. It allows a smallcurrent to control a much larger one. As youremember from our introduction to relays inChapter 2, a small amount of current flowthrough the relay coil moves an armature to openor close a set of contact points. This is called thecontrol circuit because the points control theflow of a much larger amount of current through

ker88839_ch06.qxd 1/9/06 11:25 AM Page 105

106 Chapter Six

Figure 6-28. A relay contains a control circuit and apower circuit.

Figure 6-29. When the horn button is pressed, lowcurrent through the relay coil magnetizes the core. Thispulls the armature down and closes the contacts tocomplete the high-current circuit from the battery tothe horn.

Figure 6-30. Energizing a solenoid moves its core,converting current flow into mechanical movement.(GM Service and Parts Operations)

Figure 6-31. A starter solenoid mounted onthe starter motor. Solenoid movement engagesthe starter drive with the engine flywheel gear.

a separate circuit, called the power circuit(Figure 6-28).

A relay with a single control winding is gener-ally used for a short duration, as in a horn circuit(Figure 6-29). Relays designed for longer periodsor continuous use require two control windings.A heavy winding creates the magnetic field nec-essary to move the armature; a lighter secondwinding breaks the circuit on the heavy windingand maintains the magnetic field to hold the arma-ture in place with less current drain.

SolenoidsA solenoid is similar to a relay in the way it oper-ates. The major difference is that the solenoidcore moves instead of the armature, as in a relay.This allows the solenoid to change current flowinto mechanical movement.

Solenoids consist of a coil winding around aspring-loaded metal plunger (Figure 6-30).When the switch is closed and current flowsthrough the windings, the magnetic field of thecoil attracts the movable plunger, pulling it

against spring pressure into the center of the coiltoward the plate. Once current flow stops, themagnetic field collapses and spring pressuremoves the plunger out of the coil. This type ofsolenoid is used to operate remote door locks andto control vacuum valves in emission control andair conditioning systems.

The most common automotive use of a solenoidis in the starter motor circuit. In many systems, thestarter solenoid is designed to do two jobs. Themovement of the plunger engages the starter motordrive gear with the engine flywheel ring gear so thatthe motor can crank the engine (Figure 6-31). Thestarter motor requires high current, so the solenoidalso acts as a relay. When the plunger moves into

ker88839_ch06.qxd 1/9/06 11:25 AM Page 106


Figure 6-32. A starter solenoid also acts asa relay.

the coil, a large contact point on the plunger meetsa large stationary contact point (Figure 6-32).Current flow across these contact points completesthe battery-to-starter motor circuit. The plungermust remain inside the coil for as long as the startermotor needs to run.

A large amount of current is required to draw theplunger into the coil, and the starter motor alsorequires a large amount of current. To conserve bat-

Figure 6-33. A starter solenoid, showing the pull-in andhold-in windings. (Delphi Corporation)

tery energy, starting circuit solenoids have two coilwindings, the primary or pull-in winding and thesecondary or hold-in winding (Figure 6-33). Thepull-in winding is made of very large diameterwire, which creates a magnetic field strong enoughto pull the plunger into the coil. The hold-in wind-ing is made of much smaller diameter wire. Oncethe plunger is inside the coil, it is close enough tothe hold-in winding that a weak magnetic field willhold it there. The large current flow through thepull-in winding is stopped when the plunger iscompletely inside the coil, and only the smallerhold-in winding draws current from the battery. Thepull-in winding on a starter solenoid may drawfrom 25 to 45 amperes. The hold-in winding maydraw only 7 to 15 amperes. Some starter motors donot need the solenoid movement to engage gears;circuits for these motors use a solenoid primarily asa current switch. The physical movement of theplunger brings it into contact with the battery andstarter terminals of the motor (Figure 6-34).

Buzzers and ChimesBuzzers are used in some automotive circuits aswarning devices. Seatbelt buzzers and door-ajarbuzzers are good examples. A buzzer is similar inconstruction to a relay but its internal connectionsdiffer. Current flow through a coil magnetizes a coreto move an armature and a set of contact points.However, in a buzzer, the coil is in series with thearmature and the contact points are normally closed.

ker88839_ch06.qxd 1/9/06 11:25 AM Page 107

108 Chapter Six

Figure 6-36. The motor principle.

Figure 6-35. Typical horn relay and buzzer circuits.(Delphi Corporation)

When the switch is closed, current flow throughthe buzzer coil reaches ground through the normallyclosed contacts. However, current flow also magne-tizes the buzzer core to move the armature and openthe contacts. This breaks the circuit, and current flowstops. Armature spring tension then closes the con-tacts, making the circuit again (Figure 6-35). Thisaction is repeated several hundred times a second,and the vibrating armature creates a buzzing sound.

Most simple automotive buzzers are sealedunits and simply plug into their circuits. Somebuzzers are combined in a single assembly with arelay for another circuit (Figure 6-35), such as ahorn relay. This application is used on someGeneral Motors cars. While mechanical buzzersare still in use, they are comparatively heavy anddraw a relatively high current compared to thelighter solid-state chimes and buzzers providedby electronic technology and tone generators.

MotorsThe typical automotive electrical system includesa number of motors that perform various jobs.The most common is the starter motor (also calleda cranking motor), which rotates the automobile’scrankshaft until the engine starts and can run byitself. Smaller motors run windshield wipers,power windows, and other accessories. Whateverjob they do, all electric motors operate on thesame principles of electromagnetism.

We explained the motor principle in terms ofmagnetic field interaction in Chapter 4. When acurrent-carrying conductor is placed in an exter-nal magnetic field, it tends to move out of astrong field area and into a weak field area(Figure 6-36). This motion can be used to rotatean armature. Now we will see how automotiveelectrical motors are constructed and used.

A simple picture of electric motor operation(Figure 6-37) looks much like the operation of asimple generator. Instead of rotating the loopedconductor to induce a voltage, however, we areapplying a current to force the conductor to rotate.As soon as the conductor has made a half-revolu-tion, the field interaction would tend to force itback in the opposite direction. To keep the con-ductor rotating in one direction, the current flowthrough the conductor must be reversed.

Figure 6-34. When the Ford starter relay isenergized, the plunger contact disk moves against thebattery and starter terminals to complete the circuit.

ker88839_ch06.qxd 1/9/06 11:25 AM Page 108


Figure 6-37. A simple motor.

This is done with a split-ring commutator,which rotates with the conductor as shown inFigure 6-37. Current is carried to the conductorthrough carbon brushes. At the point where cur-rent direction must be reversed, the commutatorhas rotated so that the opposite half of the splitring is in contact with the current-feeding brush.Current flow is reversed in the conductor androtation continues in the original direction. Inactual motors, many more conductor loops aremounted on an armature (Figure 6-38).

Electric motors can be manufactured with sev-eral brushes and varying combinations of seriesand parallel connections for armature windingsand electromagnetic field windings. The designdepends upon the use to which the motor will beput. Electric motors generally use electromagneticfield poles because they can produce a strong fieldin a limited space. Field strength in such a motoris determined by the current flow through the fieldwindings. The starter motor is the most commonautomotive application of this design.

Most small motors used in automotive applica-tions, however, are built with permanent magnetfields. These motors are inexpensive, lightweight,can reverse direction of operation if necessary,and can be equipped with up to three operatingspeeds. They are ideal for constant light loads,such as a small electric fan.

Regardless of how they are built, all motorswork on these principles. Understanding theinternal connections of a motor is essential fortesting and repair. Figure 6-39 shows the circuitsymbol for a motor.

WIRE COLORCODINGFigure 6-40 shows current flows through a simplecircuit consisting of a 12-volt battery for power, afuse for protection, a switch for control, and a lampas the load. In this example, each component islabeled and the direction of current is marked.Manufacturers use color coding to help techniciansfollow wires in a circuit. We have explained howmost automotive wires are covered with a coloredpolyvinyl chloride (PVC), or plastic, insulation. Thecolor of the insulation helps identify a particularwire in the system. Some drawings of a circuit haveletters and numbers printed near each wire (Figure6-41). The code table accompanying the drawing

Figure 6-38. An electric motor. (Delphi Corporation)

Figure 6-39. The electrical symbol for a motor.

Figure 6-40. Diagram of a simple circuit.

ker88839_ch06.qxd 1/27/06 5:02 PM Page 109

110

Figure 6-41. A Chrysler diagram showing circuits identified by number and wire color. (DaimlerChryslerCorporation)

ker88839_ch06.qxd 1/9/06 11:25 AM Page 110

explains what the letters and numbers stand for. ThisChrysler diagram contains code information on wiregauge, circuit numbers, and wire color. Circuit num-bers are discussed later in this chapter. Figures 6-41,6-42, 6-43, and 6-44 show how Chrysler, GM, andFord may present color-code information. Note that

the Toyota diagram in Figure 6-45 simply has thecolor name printed on the wires; wire gauge is notidentified in this drawing.

For more information about wire color coding,see the “Copper Wiring Repair” in Chapter 6 ofthe Shop Manual.

THE LANGUAGEOF ELECTRICALDIAGRAMSIn this chapter, illustrations from GM, Chrysler,Ford, Toyota, and Nissan show how different manu-facturers present electrical information. Note thatmany component symbols and circuit identificationdo not look exactly the same among different vehiclemanufacturers. Once you become familiar with thediagrams, the differences become less confusing.

Circuit NumbersIf the wire is labeled with a circuit number, as inFigures 6-41 and 6-44, those circuits are identified inan accompanying table. The top half of Figure 6-42shows the Chrysler method of identifying circuitswith a letter and number. Any two wires with thesame circuit number are connected within the samecircuit. Some General Motors service manuals con-tain current-flow diagrams developed by SPX ValleyForge Technical Information Systems; However,GM no longer uses these diagrams. Electrical circuitdiagrams are printed in color so the lines match thecolor of the wires. The name of the color is printedbeside the wire (Figure 6-46). The metric wire gaugemay also be printed immediately before the colorname. Other GM drawings contain a statement thatall wires are of a certain gauge, unless otherwiseidentified. If this is the case, only some wires in thedrawing have a gauge number printed on them.

The Ford circuit and table in Figure 6-44 arefor a heater and air conditioner electrical circuit.The wire numbers are indicated by code numbers,which are also circuit numbers. Again, no wiregauges are identified in this example.

Wire SizesAnother piece of information found in some elec-trical diagrams is the wire size. In the past, vehiclesbuilt in the United States used wire sizes specifiedby gauge. Gauge sizes typically vary from 2 for a

Electrical Diagrams 111Electrical Diagrams and Wiring 111

A 2 18 LB/YL

COLOR OF WIRE(LIGHT BLUE WITH YELLOW TRACER)

GAUGE OF WIRE(18 GAUGE)

PART OF MAIN CIRCUIT(VARIES DEPENDING ON EQUIPMENT)

MAIN CIRCUIT IDENTIFICATION

WIRE COLOR CODE CHART

STANDARDTRACER

COLOR CODE COLOR COLORBL BLUE WTBK BLACK WTBR BROWN WTDB DARK BLUE WTDG DARK GREEN WTGY GRAY BKLB LIGHT BLUE BKLG LIGHT GREEN BKOR ORANGE BKPK PINK BK or WTRD RED WTTN TAN WTVT VIOLET WTWT WHITE BKYL YELLOW BK* WITH TRACER

CIRCUIT INFORMATION

Figure 6-42. Chrysler circuit identification and wirecolor codes. (DaimlerChrysler Corporation)

Figure 6-43. GM diagrams printed in color in the ser-vice manual include this table of color abbreviations.(GM Service and Parts Operations)

ker88839_ch06.qxd 1/9/06 11:25 AM Page 111

112 Chapter Six

Figure 6-44. The GM accessory circuit is color coded by circuit number. (GM Service and Parts Operations)

DaimlerChrysler Corporation. Nissan, like othermanufacturers, often includes the symbols withits components, connector identification, andswitch continuity positions (Figure 6-51). Switchcontinuity diagrams are discussed later in thischapter. For more information about componentsymbols, see the “Copper Wiring Repair” sectionin Chapter 6 of the Shop Manual.

Figure 6-52 is a basic diagram of a ToyotaCelica sunroof control relay, which controls thesunroof motor operation. Figure 6-53 shows howthe circuit is activated to tilt the sunroof open. Thecurrent travels to the motor through relay numberone and transistor one when the “up” side of thetilt switch is pressed.

DIAGRAMSThe color codes, circuit numbers, and symbolsjust illustrated are combined to create a variety ofelectrical diagrams. Most people tend to refer toany electrical diagram as a “wiring diagram,” but

starter cable to 20 for a license plate lamp. Note thatgauge-size numbers are the reverse of physical wiresizes: a lower gauge number for heavy wires and ahigher one for light wires. Figure 6-47 shows a typ-ical circuit using 20-gauge wire.

Most vehicles built in recent years specify wiresizes by their diameter in millimeters (mm). Inthis case, a starter cable might be 32 mm while atypical circuit might be 1 mm or 0.8 mm. The wiresize appears next to the color and on the oppositeside of the wire from the circuit number, as shownin Figure 6-46. Note that the “mm” abbreviationdoes not appear in the diagram. An advantage tousing the metric system is that wire size corre-sponds directly to thickness.

Component SymbolsIt is time to add new symbols to the basiccomponent symbols list (Figure 6-48). Figures6-49A and 6-49B show additional symbols formany of the electrical devices on GM vehicles.Figure 6-50 illustrates symbols used by

ker88839_ch06.qxd 1/9/06 11:25 AM Page 112


there are at least three distinct types with whichyou should be familiar:

• System diagrams (also called “wiring” dia-grams)

• Schematic diagrams (also called “circuit”diagrams)

• Installation diagrams (also called “pictorial”diagrams)

System DiagramsA system diagram is a drawing of the entire auto-mobile electrical system. This may also properly

Figure 6-45. This Toyota diagram has no color codetable; wire color abbreviations are printed directly on thedrawing. (Reprinted by permission of Toyota MotorCorporation)

Figure 6-46. General Motors Valley Forge schematicsare provided in color with the name of the color printedbeside the wire. (GM Service and Parts Operations)

Figure 6-47. In this example from Chrysler, the “X12”in the wire code stands for the #12 part of the main cir-cuit. (DaimlerChrysler Corporation)

ker88839_ch06.qxd 1/9/06 11:25 AM Page 113

114 Chapter Six

Figure 6-48. These electrical symbols are discussedin the Classroom Manual.

be called a “wiring diagram.” System diagramsshow the wires, connections to loads, switches,and the type of connectors used, but not how theloads or switches work. Installation diagramsexpress where and how the loads and wires areinstalled. This is covered later in this chapter.Figure 6-54 shows the same warning lamp cir-cuit as Figure 6-55, but in a different format.System diagrams may cover many pages of asystem and grounds are identified for all circuits.The diagram is also organized by individual sub-systems at the top. This variation on the gridtheme is another tool to quickly locate thedesired part of the diagram. A ChryslerCorporation shop manual may not supply anentire system diagram for a vehicle, but mayinstead illustrate all circuits work. Figure 6-54shows the same warning lamp circuit asFigure 6-55 but in a different format. Systemdiagrams may cover many pages of a manual asground points are identified for all circuits(Figure 6-56). The diagram is also organizedby individual subsystems at the top. This varia-tion on the grid theme is another tool toquickly locate the desired part of the diagram.A DaimlerChrysler Corporation shop manual

may not supply an entire system diagram for avehicle, but may instead illustrate all circuitsseparately, as shown in Figure 6-57.

Schematic Diagrams

A schematic diagram, also called a “circuitdiagram” describes the operation of an individualcircuit. Schematics tell you how a circuit worksand how the individual components connect toeach other (Figure 6-55). Engineers commonlyuse this type of diagram.

Some schematics are Valley Forge diagrams,which present current moving vertically. Thepower source is at the top and the ground at thebottom of the page (Figure 6-58). Figure 6-57illustrates the circuit for a DaimlerChrysler radiosystem. Some of the wires are fully identified withtwo circuit numbers, wire gauge, and wire color.Other wires, such as the two wires connected tothe front speaker, are identified only by wire gaugeand color. The “20LGN” indicates a 20-gauge,light green wire. Figure 6-59 is the fuel economylamp circuit in a GM vehicle. Here, neither wiregauge nor wire color is indicated. The “green” and“amber” refer to the color of the lamp bulbs.

Figure 6-60 shows a Ford side marker lampcircuit. Again, wire size and color are not identi-fied. The numbers on the wires are circuit num-bers. Note that the ground wires on the front andrear lamps may not be present depending uponthe type of lamp socket used on the automobile.

SwitchesSome manufacturers, such as Nissan, extend thesystem diagram to include major switches, as inthe headlight circuit shown in Figure 6-53. Thisillustration shows the current traveling from thefuse block, through the switch, and to the head-lights. If a switch does not work properly, it causesa malfunction in the electrical system. Switch dia-grams may take extra time to understand, but theyare indispensable in testing and diagnosis.

Each connection is shown as two circles joinedby a line. The grid diagram shows which individ-ual circuits have power at each switch position.A drawing of the headlight switch is included toexplain the meaning of OFF, 1ST, 2ND, A, B, andC. Normally, a drawing of the switch action doesnot accompany the system diagram. If the switch

ker88839_ch06.qxd 1/9/06 11:25 AM Page 114

115

ENTIRECOMPONENTSHOWN

PART OF ACOMPONENTSHOWN

PARKBRAKESWITCHCLOSED WITHPARKINGBRAKE ON

FUSIBLELINK

NAME OFCOMPONENT

DETAILS ABOUTCOMPONENT ORITS OPERATION

COMPONENT CASEIS DIRECTLYATTACHED TOMETAL PARTOF VEHICLE(GROUNDED).

G103

S200

P100

G101

C103

WIRE IS ATTACHED TOMETAL PART OF VEHICLE(GROUNDED).

GROUND IS NUMBEREDFOR REFERENCE ONCOMPONENT LOCATION LIST.

SEE GROUNDDISTRIBUTIONPAGE 8A-14-0

WIRE IS INDIRECTLYCONNECTED TO GROUND.

WIRE MAY HAVE ONE ORMORE SPLICES OR CONNECTIONSBEFORE IT IS GROUNDED.

FEMALE TERMINAL

MALE TERMINAL

CONNECTOR REFERENCENUMBER FOR COMPONENTLOCATION LIST

LIST ALSO SHOWS TOTALNUMBER OF TERMINALSPOSSIBLE. C103 (6 CAVITIES)

CONNECTORATTACHED TOCOMPONENT

GRY 8

CONNECTOR ONCOMPONENTLEAD (PIGTAIL)

2 RED/YEL

79

WIRE INSULATIONIS RED WITH AYELLOW STRIPE.

.5 RED 2

.5 RED 2

.5 RED 2

1 YEL 5

1 DK GRN 19

1 RED

WIRE GAGE AND INSULATIONCOLOR ARE LABELED.

SPLICES ARE SHOWNAND NUMBERED.

CIRCUIT NUMBER ISSHOWN TO HELP INTRACING CIRCUITS.

PASS THROUGHGROMMET, NUMBEREDFOR REFERENCE.

A WAVY LINEMEANS A WIRE ISTO BE CONTINUED.

FUSIBLE LINK SIZE ANDINSULATION COLORARE LABELED.

ATO GENERATOR

PAGE 8A-30-8

CURRENT PATHIS CONTINUEDAS LABELED.THE ARROW SHOWSTHE DIRECTION OFCURRENT FLOWAND IS REPEATEDWHERE CURRENTPATH CONTINUES.

TO INSTRUMENT CLUSTERPAGE 8A-51-3

A WIRE WHICHCONNECTS TOANOTHER CIRCUIT.THE WIRE IS SHOWN AGAINON THAT CIRCUIT.

CIRCUITBREAKER

SWITCH CONTACTS THATMOVE TOGETHER

DASHED LINE SHOWSA MECHANICALCONNECTION BETWEENSWITCH CONTACTS.

Figure 6-49A. Component symbols used by GM. (GM Service and Parts Operations)

ker88839_ch06.qxd 1/9/06 11:25 AM Page 115

116

.5 LT BLU

.8 YEL 237

C216

C1

C2

TWO TERMINALSIN THE SAMECONNECTOR

DASHED LINE SHOWSA PHYSICALCONNECTIONBETWEEN PARTS(SAME CONNECTOR).

A9

D4

POWERTRAINCONTROLMODULE (PCM)

PCM CONNECTOR IDENTIFICATIONC1 - BLACK - 32 WAYC2 - BLACK - 24 WAY

ELECTROSTATIC DISCHARGE(ESD) SENSITIVE DEVICESARE INDENTIFIED. REFER TOPAGE 8A-3-0 FOR HANDLINGAND MEASURING PROCEDURES.

5 VOLTS

HEAT-ACTUATEDCONTACT

HEATINGELEMENT

WHEN CURRENT FLOWSTHROUGH COIL, CONTACTWILL TOGGLE.

UNLESS NOTED,THE RELAY WILLBE SHOWN IN ADE-ENERGIZED STATEWITH NO CURRENTFLOWING THROUGHTHE COIL.

NORMALLYCLOSEDCONTACT

NORMALLYOPENCONTACT

FUSIBLE LINK

FUSIBLE LINKCONNECTS TOSCREW TERMINAL.SHOWN SEPARATED

“BRAKE”INDICATOR(RED)

INDICATES THIS CIRCUITCONTINUES WITHIN DEVICE;I.E. OTHER BULBS

AN INDICATORWHICH DISPLAYSTHE LIGHTEDWORD “BRAKE”

3 BLK 150

1 ORN 40

1 ORN 40 .5 ORN 40

G200

SEE GROUNDDISTRIBUTIONPAGE 8A-14-0

INDICATES THATTHE CIRCUITRY ISNOT SHOWN INCOMPLETE DETAILBUT IS COMPLETE ONTHE INDICATED PAGE

C309C309

GAUGES NO GAUGESWIRE CHOICSFOR OPTIONSOR DIFFERENTMODELS ARESHOWN AND LABELED.

RADIOFUSE10 AMP

DIODEALLOWS CURRENTTO FLOW IN ONEDIRECTION ONLY

FUSEBLOCK

LABEL OFFUSE BLOCKCONNECTORCAVITY

INDICATES THATPOWER ISSUPPLIED WITHIGNITION SWITCHIN “ACCY” AND“RUN” POSITIONS

HOT IN ACCY OR RUN

C210

B M D

3 CONNECTORS ARESHOWN CONNECTEDTOGETHER AT AJUNCTION BLOCK.FOURTH WIRE ISSOLDERED TO COMMONCONNECTION ONBLOCK.

NUMBER FOR TOTALCONNECTOR

LETTERS FOR EACHCONNECTION TERMINAL

Figure 6-49B. More component symbols used by GM. (GM Service and Parts Operations)

ker88839_ch06.qxd 1/9/06 11:25 AM Page 116

117

+

–

BATTERY

FUSIBLELINK

FUSE CIRCUITBREAKER

GENERATORSTATORCOILS 2 C123

2 C1234 C1 6 C3

2 C123

IN-LINECONNECTORS

58

MULTIPLECONNECTOR

MALECONNECTOR

FEMALECONNECTOR

BATT A0

HOT BAR CHOICEBRACKET

(8W-30-10)

PAGEREFERENCE

SINGLEFILAMENTLAMP

DUALFILAMENTLAMP

ANTENNA

TONEGENERATOR

NPNTRANSISTOR

PNPTRANSISTOR

SCREWTERMINAL

GROUND

G101

CLOCKSPRING

OPENSWITCH

CLOSEDSWITCH LED PHOTODIODE DIODE ZENER

DIODE

OXYGENSENSOR

GAUGE PIEZOELECTRICCELL

GANGEDSWITCH

SLIDINGDOORCONTACT

A

A

WIREORIGIN &DESTINATIONSHOWNWITHINCELL

WIREDESTINATIONSHOWN INANOTHER CELL

RESISTOR

POTENTIOMETER

VARIABLERESISTOR

HEATERELEMENT

+NON-POLARIZEDCAPACITOR

POLARIZEDCAPACITOR

VARIABLECAPACITOR

S350

EXTERNALSPLICE

INTERNALSPLICE

INCOMPLETESPLICE

(INTERNAL)

MM MONESPEEDMOTOR

TWOSPEEDMOTOR

REVERSIBLEMOTOR

COIL SOLENOID SOLENOIDVALVE

Figure 6-50. Component symbols used by DaimlerChrysler. (DaimlerChrysler Corporation)

ker88839_ch06.qxd 1/27/06 5:02 PM Page 117

118

LIGHTING SWITCHINTERNAL CONNECTIONS

OFF 1ST 2ND

A B C A B C A B C

55

6

67

8

8

9

9

10

10

11

12

7

CONNECTORFROM LIGHTSWITCH

SWITCH POSITIONS {

INDIVIDUAL

{CIRCUITS

LIGHTING SWITCH POSITIONS1ST = PARKING LIGHTS2ND = DRIVING LIGHTS

A = HIGH BEAMSB = LOW BEAMSC = FLASH (HIGH BEAMS)

LIGHTING SWITCH CIRCUITS5, 8 & 11 = POWER6 & 9 = HIGH BEAMS7 & 10 = LOW BEAMS12 = PARKING LIGHTS (NOT SHOWN)

Figure 6-51. This diagram of a headlight circuit includes the headlight switch internal connections. (Courtesy ofNissan North America, Inc.)

Figure 6-52. The advance computer technologymakes logic symbols like these a typical part of anautomotive wiring diagram.

Figure 6-53. This circuit uses logic symbols toshow how the sunroof motor operates to tilt themechanism open.

ker88839_ch06.qxd 1/9/06 11:25 AM Page 118

119

Figure 6-54. A system diagram for a warning lamp circuit.

ker88839_ch06.qxd 1/9/06 11:25 AM Page 119

120

Figure 6-55. A schematic diagram for a warning lamp circuit.

ker88839_ch06.qxd 1/9/06 11:25 AM Page 120


Figure 6-56. Toyota system diagrams are organized by individual systems and include ground points. (Reprintedby permission of Toyota Motor Corporation)

positions are not clear, find that information else-where in the electrical section of the manufac-turer’s shop manual.

Installation DiagramsNone of the diagrams shown so far have indi-cated where or how the wires and loads areinstalled in the automobile. Many manufacturersprovide installation diagrams, or pictorial dia-grams that show these locations. Some original

equipment manufacturers (OEM) call these dia-grams product description manuals (PDMs).Figures 6-61 and 6-62 show different styles ofinstallation diagrams that help locate the generalharness or circuit.

The DaimlerChrysler installation diagram inFigure 6-61 includes the wiring for radio speakers.The circuit diagram for the speakers was shown inFigure 6-57. Compare these two diagrams andnotice that the installation diagram highlights thelocation of circuits while the circuit diagram givesmore of a detailed picture of the circuit.

ker88839_ch06.qxd 1/9/06 11:25 AM Page 121

122 Chapter Six

Figure 6-57. DaimlerChrysler radio circuit. (DaimlerChrysler Corporation)

Figure 6-62 is a GM installation diagram for thefuel-economy indicator switch. The circuit dia-gram for this accessory was given in Figure 6-59.Compare these two diagrams and note that theinstallation diagram focuses on the harness and cir-cuit location while the schematic diagram shows aspecific circuit current reading top to bottom.

Troubleshooting withSchematic DiagramsIt is quicker and easier to diagnose and isolatean electrical problem using a schematic diagramthan by working with a system diagram, because

schematic diagrams do not distract or confuse withwiring that is not part of the circuit being tested.Aschematic diagram shows the paths that electricalcurrent takes in a properly functioning circuit. It isimportant to understand how the circuit is supposedto work before determining why it is malfunction-ing. For more information about troubleshootingwith schematic diagrams, see the “Copper WiringRepair” section in Chapter 6 of the Shop Manual.

General Motors incorporates a special trou-bleshooting section in each shop manual for theentire electrical system, broken down by indi-vidual circuits (Figures 6-48 and 6-60). Eachschematic contains all the basic informationnecessary to trace the circuit it covers: wire size

ker88839_ch06.qxd 1/9/06 11:25 AM Page 122

123

5 ORN 1240 1 BRN 241

1 BRN 241

.8 BRN 2415 ORN 1240

ORN 1240

GRY 292

5 PPL 293

PPL 293

PNK 241

BLK 650

.35 BLK 650

3 BLK 1150 (W/ C49)

3 BLK 1750

.5 BLK 1150 (W/O C49)

3 BLK 650

1 BRN 241

POWERDISTRIBUTIONCELL 10

POWERDISTRIBUTIONCELL 10B3

A3

DEFOG/SEATSCKT BRKR 1230 A

HVACFUSE 620 A

HOT AT ALL TIMES HOT IN RUN

F2

E2

I/PFUSEBLOCK

REARDEFOGGERTIMER/RELAY

REARDEFOGGER

GRID

REAR DEFOGGERSWITCH

HVACCONTROL

TO DRIVER POWERSEAT SWITCHCELL 140, 141

3 ORN

1240S252

C4

C6

C6

C6

C5

C5

C4

C5

C5

TO HVAC CONTROLSELECTOR SWITCHCELL 63, 64

A C

PNK

241

BRN

293

3 PPL

293

3 PPL

293

3 PPL

293

3 PPL

293

3 BLK

1150

BLK

650

4 3

(MOMENTARYCONTACT)

2

IGN ON/OFFINPUT

GROUNDDEFOGENABLE

SOLID STATE

1

ONINDICATOR

B D

CONV COUPE

COUPE

A

A

A

A

C320

C330

S420

S315

S216

G200

G320 G310

P300

GROUNDDISTRIBUTIONCELL 14

GROUNDDISTRIBUTIONCELL 14

D

CONVER-TIBLE

Figure 6-58. This diagram shows a backlight/rear window/heater circuit. Power flows from top to bottom,which is typical of a SPX-Valley Forge current flow diagram. Only components or information that belong to thisspecific circuit are shown. (GM Service and Parts Operations)

ker88839_ch06.qxd 1/9/06 11:25 AM Page 123

and color, components, connector and groundreferences, and references to other circuits whennecessary. In addition, a quick summary of sys-tem operation is provided to explain what shouldhappen when the system is working properly.

124 Chapter Six

Figure 6-59. GM fuel-economy lamp circuit. (GMService and Parts Operations)

Figure 6-60. GM Cadillac Deville side marker lamp circuit. (GM Service and Parts Operations)

GM and includes a power distribution diagramas one of the first overall schematics for trou-bleshooting (Figure 6-64). The power distributiondiagram represents the “front end” of the overallelectrical system. As such, it includes the battery,starter solenoid or relay, alternator, ignitionswitch, and fuse panel. This diagram is useful inlocating short circuits that blow fusible links orfuses, because it follows the power distributionwiring to the first component in each major circuit.

SUMMARYMany of the conductors in an automobile aregrouped together into harnesses to simplify theelectrical system. The conductors are usuallymade of copper, stainless steel, or aluminum cov-ered with an insulator. The conductor can be asolid or single-strand wire, multiple or multi-strand wire or printed circuitry. The wire size orgauge depends on how much current must be car-ried for what distance. Wire gauge is expressed asa number—the larger the number, the smaller thewire’s cross-section.

ker88839_ch06.qxd 1/9/06 11:25 AM Page 124

Cars use some special types of wire, especiallyin battery cables and ignition cables. Terminalsand connectors join different wires in the car;these can join single wires or 40 or more wires.Part of every automotive circuit is the ground paththrough the car’s frame and body. The battery ter-minal that is connected to ground determines theelectrical system’s polarity. Most modem auto-mobiles have a negative-ground system.

Multiplexing simplifies wiring by sending twoor more electric signals over a single channel.Along with conductors, connectors and theground path, each automotive circuit has control-ling or working parts. These include switches,relays, solenoids, buzzers and motors.

There are three types of electrical circuit dia-grams: system, schematic, and installation. Systemdiagrams typically present an overall view, whileschematic diagrams isolate a single circuit and are

more useful for troubleshooting individual prob-lems. Installation diagrams show locations andharness routing. To better understand these dia-grams, a variety of electrical symbols are used torepresent electrical components. Other tools to aidin successfully reading these diagrams are thecolor coding and the circuit numbering of wires,which identify the wire and its function.Manufacturers publish diagrams of each vehicle’selectrical systems, often using these color codesand circuit numbers. A technician cannot servicea circuit without knowing how to read and usethese diagrams.


Figure 6-61. DaimlerChrysler installation diagram.(DaimlerChrysler Corporation)

Figure 6-62. GM installation diagram. (GM Serviceand Parts Operations)

Continues onpage 22-18

DASHBOARD WIRE HARNESS B

1

2

3 4 5 6 7

8

9

1011121314

PASSENGER’SUNDER-DASHFUSE/RELAYBOX

Figure 6-63. Acura installation diagram. (Courtesy ofAmerican Honda Motor Co., Inc.)

Figure 6-64. A typical GM power distributionschematic. (GM Service and Parts Operations)

ker88839_ch06.qxd 1/9/06 11:25 AM Page 125

126 Chapter Six

Review Questions1. Which of the following is not considered

part of the primary wiring system of anautomobile?a. Spark plug cablesb. Lighting circuitsc. Accessory wiring circuitsd. Power distribution circuits

2. Automotive wiring, or circuit conductors,exist as all of the following, except:a. Single-strand wireb. Multistrand wirec. Printed circuitryd. Enameled chips

3. Which of the following wires are known assuppression cables?a. Turn signal wiringb. Cables from the battery to the starter

motorc. Cables from the distributor cap to the

spark plugsd. Wiring harnesses from the fuse panel to

the accessories

4. High-resistance ignition cables are used todo all of the following, except:a. Reduce radio frequency interferenceb. Provide extra resistance to reduce

current flow to the spark plugsc. Provide more current to the distributord. Boost the voltage being delivered to the

spark plugs

5. One of the most common wear points in anautomobile electrical system is:a. At the ground connecting sideb. The point where a wire has been bentc. Where two connectors have been

joinedd. At a Maxifuse connection

6. The symbol below indicates which of these:

a. Batteryb. Capacitorc. Dioded. Ground

7. Which of the following is not a term used todescribe an automobile wiring system?a. Hot-return systemb. Single-wire systemc. Ground-return systemd. Negative-ground system

8. For easy identification, ground wires onmost automotive electrical systems arecolor-coded:a. Redb. Whitec. Blackd. Brown

9. Which of the following is not used to switchcurrent flow?a. Relayb. Solenoidc. Transistord. Coil Windings

10. Two separate windings are used in startersolenoids to:a. Increase resistance in the circuitb. Decrease resistance in the circuitc. Increase current being drawn from the

batteryd. Decrease current being drawn from the

battery

11. Which of the following reverses the flow ofcurrent through the conductor of a motor?a. The armatureb. The terminalsc. The field coilsd. The commutator

12. The symbol shown below is for which ofthese:

a. Fuseb. Relayc. Motord. Resistor

13. Which of the following is NOT used to protecta circuit from too much current flow?a. Fuseb. Buss bar

ker88839_ch06.qxd 1/9/06 11:25 AM Page 126


c. Installation diagramd. Alternator circuit diagram

20. Automobile manufacturers color-code thewires in the electrical system to:a. Help trace a circuitb. Identify wire gaugec. Speed the manufacturing processd. Identify replacement parts

21. A wire in a Valley Forge (system) diagram isidentified as .8 PUR/623 which of thefollowing:a. 8-gauge wire, power plant, circuit

number 623b. 8-gauge wire, purple, vehicle

model 623c. 0.8-mm wire, purple, circuit number 623d. 0.8 points per length, vehicle model 623

22. Which of the following electrical symbolsindicates a lamp?

a.

b.

c.

d.

23. Two technician are discussing the meaningof different types of wiring diagrams.Technician A says schematic diagrams tellyou how a circuit works and how theindividual components connect to eachother and they are commonly used byengineers. Technician B says a systemdiagram is drawing of a circuit or any part of

c. Fusible linkd. Circuit breaker

14. What usually causes a fuse to “blow”?a. Too much voltageb. Too much currentc. Too little voltaged. Too little resistance

15. Fuses are rated by __________ capacity.a. Currentb. Voltagec. Resistanced. Power

16. Which of the following is true of circuitbreakers?a. Made of a single metal stripb. Must be replaced after excess current

flowc. Less expensive than fuses ared. Used for frequent temporary overloads

17. This symbol represents which of these items:

a. Circuit breakerb. Variable resistorc. Capacitord. Solenoid

18. The following two symbols represent whichtwo devices?

a. Zener diode and a PNP transistorb. Zener diode and a NPN transistorc. One-way diode and a PNP transistord. One-way diode and a NPN transistor

19. The electrical diagram that shows where thewires and loads are physically located onthe vehicle is the:a. Schematic diagramb. Electrical system diagram

ker88839_ch06.qxd 1/9/06 11:25 AM Page 127

128 Chapter Six

a circuit that shows circuit numbers, wiresize, and color-coding. Who is right?a. A onlyb. B onlyc. Both A and Bd. Neither A nor B

24. Technician A says the battery cableprovides a connection from the vehiclechassis to the battery. Technician B saysthat automotive electrical systems arecalled double-wire or positive returnsystems. Who is right?a. A onlyb. B only

c. Both A and Bd. Neither A nor B

25. Technicians are discussing wiregauge sizes. Technician A says wiresize numbers are based on the cross-sectional area of the conductor andlarger wires have lower gaugenumbers. Technician B says wirecross-section is measured in circular rods.Who is right?a. A onlyb. B onlyc. Both A and Bd. Neither A nor B

ker88839_ch06.qxd 1/9/06 11:25 AM Page 128

Chapter 06

Documents

Transcript of Chapter 06