Trailer Wiring

Ultimate trailer wiring diagram and electrical trouble shooting information for your trailer. Complete wiring diagrams for 4 way, 5 way, 6 way & 7 way flat

connectors.

Before you are able to legally tow your trailer on the road, you’ll need to make sure your trailer lights are installed and working properly. This step not only

ensures that you will not get pulled over and ticketed, but also significantly reduces your chances of getting into an accident. While most trailers come with thelighting and wiring already installed, we’ll cover some of the basics about the wiring/electrical systems on your trailer in the event you ever need to

troubleshoot issues, or purchase a replacement. In the event your vehicle was not designed for easy towing, we’ll also cover your options for tapping intoyour existing vehicle wiring harness to install a towing connector

Trailer Wiring Connectors: The Basics

Trailer wiring connectors are available in systems ranging from four to seven wires/pins that transfer power to the basic lighting and brake functions, as well as

additional functions such as backup lights, interior trailer lights, or auxiliary sources requiring power such as a winch. As such, you need to choose your wiring

connector based on the number of functions of your trailer. As is often the case, the connecter sits under your vehicle – if this is the case, you need to use a

mounting brackets to properly attach it. Each wire/pin is color coded based on what function it is typically designed to accommodate:

Four-Way Connectors

Four-Way connectors typically allow for the three basic functions: running lights, braking lights, and turn signals – the fourth wire is used as the ground wire.

The four-way connector is often used in standard light duty trailers. The Four-Way connectors in most lighting kits are known as a flat connector – with three

male ends and one female end. The connector is designed this way to eliminate the possibility of the user plugging it is backwards.

4 Way Flat Tow Vehicle End

4 Way Flat Tow Vehicle End

Five-Way Connectors

Five-Way connectors allow for the same three functions as the four-way connector (i.e. running lights, braking lights, and turn signals) but also add one more

wire to support an additional function in addition to the grounding wire. The five-way connector is most commonly used in trailers that utilize either surge orhydraulic brakes – as the additional wire is connected to the reverse lights to disengage the actuator – thus disengaging the brakes – when the vehicle is

backing up.

5 Way Flat Tow Vehicle End

5 Way Flat Tow Vehicle End

Six-Way Connectors

Six-Way connectors allow for the same three functions as the four-way connector (i.e. running lights, braking lights, and turn signals) but also add two extra

wires for additional functions – typically for both an electric braking system and a 12 volt lead for running an additional feature such as a winch or interior

lighting system. The six-way connector is commonly seen in a vehicle such as a camper, where more accessories needing electricity are present.

6 Way Flat Tow Vehicle End

6 Way Flat Tow Vehicle End

Seven-Way Connectors

Seven-Way connectors allow for the same three functions as the four-way connector (i.e. running lights, braking lights, and turn signals) but also add three

additional wires for electric braking systems, a 12 volt lead, and an additional feature such as backup lights. There are two primary styles of seven-way

connectors – one utilizing flat pins and the other utilizing round pins. The vast majority of seven-way connectors utilize the flat pin model.

7 Way Flat Tow Vehicle End

7 Way Flat Tow Vehicle End

7 Way Round Tow Vehicle End

7 Way Round Tow Vehicle End

Mounting your Trailer Wiring Harness

When not being used, the trailer wiring harness is often left in the vehicle to help ensure the integrity of the connector by protecting it from the weather. When

needed, the user would simply take the connector out. In the event you need to connect underneath your vehicle, you can use one of many different mountingbrackets to both protect the connector and hold it in place.

Wiring Adaptors

Most of the smaller utility trailers use a four-pole connector. In the event this is not compatible with your needs, the four-way connector is easily adaptable toaccommodate the larger five-way, 6-way, and 7 way styles. An adapter will simply plug into the four-way connector and add additional wires to accommodateadditional functions such as utility lights, reverse lights, or an auxiliary source for powering things such as a winch. By using an adapter, you avoid the hassle –

and expense - of having to splice into the wiring system of your vehicle.

In addition to the four-pole connector adapter, we carry a wide variety of adaptors for other size connectors.

Common Wiring Problems

Below are some of the most commonly encountered problems. Of course, please feel free to contact us if you have any additional questions.

The converter is not working properly

First, before you are able to troubleshoot your issue you must be able to discover where the problem is arising – this can be accomplished by using a circuittester. If you have a circuit tester, you must then use it to see if there is power going to and from the converter box without the trailer hooked up. From here,there are four common problems you may encounter:

1. Something is wrong with the vehicle and, as a result, there is no signal going into the box. If you encounter this issue, first check to see if there are anyblown fuses. If not, you can then use the circuit tester to make sure the correct wires are attached. You may also want to make sure that the harnessconnectors are plugged into the right connections on your vehicle and that these connecters are plugged in properly.

2. There is a problem with the trailer wiring if a signal is going in and coming out the correct wires in the converter box. Before doing anything else, check tosee if the ground wire on the trailer is secured properly. On most trailers, the wiring system is grounded to the frame right next to the coupler. This ground

wire is typically white. In addition, each light also needs to be grounded individually. The ground wires to the lights will either be grounded via a whitewire coming out of the individual light, or it will be mounted inside via its studs. While doing this, also make sure that the ground is attached to the metalframe and is not being hindered by dirt, rust, paint, etc. If this does not solve the problem, check the wiring on the trailer to ensure everything is connected

properly. It also may be helpful to check the wires for any damage such as cuts or pinches that may affect their functionality.3. The ground on the vehicle is not connected properly, resulting in either (a) a signal going into the converter and coming out the wrong wire, or (b) a signal

coming into the converter and not coming out at all. This problem can be fixed by checking the ground wire on your vehicle to make sure it has been

properly placed. Again, you will need a circuit tester to accomplish this. First, you will need to connect the ground wire of the circuit tester at the sameplace as the wiring harness’ ground wire and test the signal. If there is no signal, then attach the circuit tester’s ground wire to another locationsuch as your vehicle’s exhaust pipe. If you are able to get a signal now, the initial ground location is no good. Try another spot – again, make sure

that the new grounding spot is attached to the metal frame and is not being hindered by dirt, rust, paint, etc.4. The wiring harness has simply shorted out or is simply defective. While the latter is fairly rare, the former can occur if there are problems with the trailer

wiring. If you are dealing with a shorted out wiring harness, make sure you fix the wiring issues before installing a new one. See right below for moreinformation about a shorted out converter.

The Converter has shorted out

The converter can short out when too much power (amps) are put through it at one time. This can occur when:

1. The connectors on your trailer get wet. This most commonly occurs when you back a boat trailer into the water while the trailer wiring is still connected tothe vehicle, but it can also happen in very heavy rain. To prevent this, ALWAYS disconnect the trailer connections from your vehicle before backing itinto the water.

2. You’ve attached more lights on your trailer than the converter can handle. A standard converter is able to accommodate 4 amperes passing throughit at a time – as such, a standard box is not able to accommodate more than one taillight on each side.

3. Wires are touching either each other or the bare metal trailer frame. Check to see if the wires have gotten pinched in any places, or if the wire coating hasdeteriorated anywhere along the wiring system.

Inadequate Ground

You will know you have a grounding issue if some, but not all of the lights are working. You can check this by using both the taillights and brake lights at thesame time – as this will require the maximum amount of amperes to pass through the trailer lights, making the weak ground show itself if it is a problem.

You can fix this problem by checking the ground wire. On most trailers, the wiring system is grounded to the frame right next to the coupler. This ground wire is

typically white. In addition, each light also needs to be grounded individually. The ground wires to the lights will either be grounded via a white wire coming outof the individual light, or it will be mounted inside via its studs. If the lights are mounted on PVC pipe or wood, they will not be able to be properly grounded.While doing this, also make sure that the ground is attached to the metal frame and is not being hindered by dirt, rust, paint, etc. If this does not solve the

problem, check the wiring on the trailer to ensure everything is connected properly. In some cases involving tilting bed trailers, the ground is weak because it isnot able to pass through the pivot point. If this is your problem, you need to send the ground wire from the connector at the front of the trailer to each separatelamp assembly at the back to bypass this pivot point.

How can I wire my vehicle to pull a trailer?

As mentioned above, before you are able to legally tow your trailer, you need to have – at a minimum – tail lights, brake lights, and turn signals. Most

trucks, vans, SUVs and RVs made since the mid-1990s include factory installed trailer lighting connectors. If your vehicle is not already equipped to handle awiring assembly, you have two options for splicing into your vehicles electrical system: (1) a T-One Connector and (2) a customized hardware kit.

The T-One Connector is by far the easiest way to make your vehicle tow-ready. The T-One connector comes with OEM connections that plug directly into the

wiring harness of your vehicle. Your vehicles wiring harness is likely located either (1) near the rear of your vehicle, (2) directly next to the tail lights, (3)underneath the vehicle, or (4) behind the paneling in the rear cargo area. The T-One connector is pre-wired for a four-way flat connection – but this can bealtered via an adapter (see above).