How To Wire A 7 Way Plug On A Truck? [Easy Steps]

One of the important connectors in your truck is the 7 way pin plug. Wiring a 7 way pin plug may seem a little difficult and complicated to you if you do not observe it very closely.

Notice that your truck has a lot of wires attached to the wiring harness. Don’t panic when you see all this, because it is relatively easy to do if you know the right way and its effectiveness. Since different truck models are designed differently and differently, you should have a definite repair or service manual.

The manual includes a 7 way pin plug wiring diagram for the truck of your particular model. Basically, you need to know the meaning of the wires of different colours. In this article, we are going to learn how to wire a 7 way pin plug on a truck in a very simple way.

Cautions About Wiring A 7 Way Plug on a Truck

When you are going to do a 7 way plug wiring on your truck, you need to be aware of some cautions. Such as:


If you want to install a harness while your truck has a warranty, we recommend that you consider wiring the 7 way plug on your truck by a professional. It is because if you do an aftermarket plug wiring on your truck, the warranty on the truck’s electrical equipment may be void.

Color Code

Another concern about the 7 way plug wiring is knowing the colour code of the harness. Each colour has different functionality. You must do the wiring on the right pin of the right colour.

Colour codes carry different meanings in different industries. 

For example, the Society of Automotive Engineers (SAE) standard wiring differs from the standard wiring in the Recreational Vehicle (RV) industry.

Let’s take a look at the values of both types of harnesses:

SAE Standard

  • Green: Right turn/brake light
  • Blue: Brake controller output
  • Black: Battery hot lead
  • Yellow: Left turn/brake light
  • White: Ground wire
  • Brown: Tail/running lights
  • Purple: Reverse lights

RV Standard

  • Green: Tail/running lights
  • Blue: Brake controller output
  • Black: Battery hot lead
  • Yellow: Reverse Lights
  • White: Ground wire
  • Brown: Right turn/brake light
  • Red: Left turn/brake light

Wire Gauge

We suggest you use the minimum 16 gauge wire for the turn signal, brake light, reverse light and moving light of your 7 way trailer plug. On the other hand, pick up a minimum of 12 gauge wires for your truck’s ground, brake power, and battery hot lead.

How To Wire a 7 Way Plug on A Truck?

So let’s take a look at the main task, i.e. how to do 7 way plug wiring on your truck and trailer step by step.

Wiring the Trailer Side

First of all, we will learn how to do a 7 way plug wiring on your trailer.

Step 1: Preparation

Before you start your trailer wire make sure you have everything you need, such as a junction box to protect the wiring, a brake controller, and a breakaway kit.

Step 2: Locate the Junction Box or Install A New One

If your old trailer already has a junction box, locate it and remove the cover. Unscrew the nut from each terminal of the junction. 

On the other hand, if you want to install a new junction box in your trailer, find a suitable location where the installation can be done. It could be on the inside edge of your trailer tongue. However, make sure that the junction box is close enough that the wires reach it.

Suppose you don’t have a junction box or you don’t want to install it, then? The solution is to mount a new cable harness to the existing cable in your trailer.

Step 3: Make Trailer Connections

If You Want to Do with A Junction Box:

Unscrew the nuts in each junction box stud. If you are replacing an old 7 way plug wiring, remove the old wires with each terminal from the junction box. Take a moderate amount of wire and remove the insulators using a crimper. 

Then, clamp the ring terminal to the front of the new cable. Place the terminals in the corresponding studs in the junction box, i.e. place them on specific studs, such as brake wire to brake wire, ground wire to ground wire, etc. When done, re-screw the nuts. If extra wires come out, secure them with wire clips.

If You Don’t Want to Do with A Junction Box:

All you can do is use a hitgun and butt connector to make your cable connections. As before, if extra wires come out, secure them with wire clips.

Wiring the Vehicle Side

Since you have successfully wired the 7 way plug on your trailer, now let us know how to do 7 way plug wiring on your truck.

Step 1: Preparation

If you already have a 7-way connector on your truck, just connect or plug in the trailer-end connector and the car’s end connector without much fuss.

However, if your car has a 4-way connector, the easiest way to attach it to the trailer’s 7-way plug is to use an adapter kit, such as the ETBC7. This will convert your 4 way to 7 way. Before connecting, activate each function, such as brake light, turn signal, etc., and make sure you have the correct cable.

If your car does not have any kind of connector, it would be easier to use an adapter with a 4 way install than a 7 way plug. Before connecting a 4-way plug, make sure each cable is functional and check your track’s manual for this.

Step 2: Making Connection

The type of connection will depend entirely on the model of your vehicle whether it will be plugged in, clamped onto, or splice into.

4 Way Plug to 7 Way Plug

Turning a 4 way plug into a 7 way plug requires an ETBC7 kit as it includes everything from wiring, connectors and circuit breakers to installing a 7 way adapter. 

Now you plug the adapter in the 4 way. At this time, you will have three extra wires which must be connected like others. One of these wires, the colour of which is usually blue, but sometimes black, will be connected to the truck’s electric brake control power output. 

Another black or red wire will connect to the positive terminal of the battery via the butt connector and additional wires. Be sure to use a circuit tester to test the functionality before connecting all the wires.

Plug-in Style

Some vehicle manufacturers have pre-wired wiring in your vehicle to make the wires easier to connect. In this case, plug the T-connectors into the supplied wiring of your truck. You don’t even have to cut or disassemble. 

To access the plug you may need to remove your scaffold panel, trim access cover, taillights, etc. as the plug-in connection is usually mounted under the car or behind the rear cargo panelling or near the taillights.

Where Does the Black Wire Go on A 7 Way Plug?

The black wire goes to the 12-volt hot lead on a 7 way plug.

Does a 7 Pin Connector Control Brakes?

Yes, a 7 pin connector control brakes. This type of control has a 12-volt circuit and the brake controller has to be mounted to prevent the brake.

Are All 7 Pin Trailer Plugs the Same?

In general, there are two different types of 7 way connectors- one is a flat pin and the other is a round pin. Round pin connectors are very rare. On the other hand, flat pins are common and are often found in new SUVs and trucks.


So, all the ways to do a 7 way plug wiring on a truck are described step by step in this article. You can easily attach the truck to your trailer by following the steps properly. But remember, if you get stuck somewhere while completing the task, there is no option but to seek professional help.

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