Trailers need to be wired to improve the safety of your passengers, the cargo, and other motorists as well. It is a legal and a safety requirement for your trailer to have running lights, turn signals, and brake lights. You need to know how to wire trailer lights template by locating the vehicles wiring harness, getting the correct adapters and pin connectors.

Using a 7 pin or 4 pin connector depends on the number of extra connections needed. Using a 4 pin connector is able to handle the basic lighting. The extra lightings that may be needed are the trailer's brake lights and reverse lights. This article aims to take you through the wiring of a trailer light plug and the steps you need to follow to wire a trailer harness.


What You Will Need

1. ​Cables

Depending on the number of lightings needed, you may require extra cables to run through the harness

2. Adapters​

They are used to connect cables to the pin connectors to ensure connectivity

3. Connection Sets and Plugs​

They are used to add connectivity from the junction box

4. T- One Connector​

The main connection point between the trailer and the car rear

5. Car Owner’s Manual

For making reference to the harness circuit diagram if available

6. A drill​

A drill will be helpful for drilling holes to allow wires to pass through

7. Distributors​

Needed for connecting all light functions from the front panel to the rear ends. Distributors are also required for additional lighting.​

What to do

Step #1: Locating the Wiring Harness

The wiring harness is vital when you want to connect the trailer lights to the vehicle lighting system. The harness is located near the rear door. In some vehicles, the wiring harness is located in the trunk. In some cases, the harness is found next to the rear tail lights. If you are unable to locate the harness of your vehicle, please consult your owner’s manual. The manual shows how to locate and retrieve the harness.

Step #2: Connecting the Harness

If in your scenario you cannot use the T- one connector to attach the trailer to the vehicle's rear end, you may consider using the connectors. Different types of connectors are available for this purpose. You will need a T-one connector or a custom hardware kit​.

Step #3: Running the Light Cable​

From the front of the trailer, locate a semi-rigid section of the steel wire and pull it through the drilled hole on the inside of the drawbar. The drawbar is found next to the spring end. Bind the trailer core cable wire to the end of the steel wire and pull it until the cable is visible.

Step #4: Fit the Junction Bar​

The junction bar is located above the spring hanger. Wire the cable to the strip connector and run the cable from the junction box through the entire length of the chassis rail to the light channel. The junction box plays a vital role in that all the other cabling requirements such as marker and electric brake lights can be drawn from the junction box.​

NOTE: You may need to drill some holes to allow the cable to pass through as needed.​

Step #5: Fitting the Lights​

  • Mark the position of your light fitting in order to get the correct position. Make sure that you place your lights as wide as possible on the light channel.
  • Mark the light position and drill the mounting holes according to the light template. There are two ways in which you can join the wires behind the left and right light.
  • One way is the use of the strip connectors found on the junction box. This method ensures a secure water tight connection and also gives an easier option when it comes to replacing lights.
  • The second option is soldering the wire together and using an insulation tape and a heat sink tubing. The good thing about the second option is the little time it takes to set up, but it makes it difficult to do maintenance repairs.​

Step #6: Front Marker Lights

The front marker lights require additional cables that need to run from the junction box, and along the length of the trailer to the front marker position.

Step #7: Installing the Plug​

Slide the plugs over the cables to make sure that each cable goes in the correct sequence as per the socket diagram. Tighten the screws but do not over tighten and screw the cable clamp to prevent cable tugging. Make sure that the cables passing through the trailer are well trimmed so that the cables can move with the trailer without being stretched or tugged. The length should also not be too long to dangle too close to the ground.​

Different Methods of Connecting the Harness

The harness can be connected through various methods; you can use the T-One connectors or a custom hardware kit.

The T-One Connectors​

Using the T-One connector should be the easier way to make a link between your car and trailer. Every car model can either have a 4-pin trailer connector or have adapters that can allow them to be hooked to 5, 6, or 7 pin connections.

Custom Hardware Kits​

Customized hardware are appropriate for cars with no T-One connectors. Most of this connectors can be found in any auto shop. One important aspect of a custom hardware is whether you need your trailer to have separate signals for the turn and brake lights.​

Other Types of Connectors

Despite the fact that T-One connectors and the 4-pin are the commonly used in trailer lighting, you should know that other connectors are also available. It is imperative that you use the best connector to enjoy additional features such as brake lights and hot lead.

7-Pin Connectors​

This connector has three extra connection points that allow you to install electric brakes, backup lights, and hot lead. The connectors may be rounded or flat pin heads.

6-Pin Connectors​

Contains two additional pins that are commonly used to control trailer brakes and 12-volt hot lead. Can also be found as flat or round pins.

5-Pin Connectors​

The 5-Pin connector has an extra fifth pin reserved for handling surge or hydraulic brakes on a trailer. The 5-pin connector works as a vehicle’s backup lights and disables the brakes when reversing.

4-Pin Connectors​

This connector is considered to be the core connector that can handle all the essential functions of trailer wiring. Each pin has a dedicated function. The core functions include the running lights, brake lights, turning lights and ground functions.


Wiring your trailer should now be an easy task if you follow keenly on the steps explained above. Getting the intricacies involved in the wiring process need a careful approach. For you to understand how to wire trailer light template, you can make use of the circuit diagrams found on the internet or on the harness diagrams.

If you are forced to install the trailer connector beneath, the vehicle, purchase a mounting bracket. The mounting bracket protects the connectors and keeps them from hanging beneath the car.

If you choose to use the custom made connectors go for one with the appropriate number of pins that relates the type of trailer lighting you need. To avoid being disappointed make sure you purchase wire extensions and adapters just in case you need them.

I hope that you now have the confidence and enough information to complete the trailer wiring process all by yourself. If you encounter any challenges along the way feel free to share through the comment section. You can also share the article to help the others get it right!

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Chief editor at Paul's Gigantic Garage. I came up with this blog to help you to sort out some basic problems your car may be facing and in turn, save lots of cash by some of my DIY tips that I hope will get your car out of its current situation. I also had in mind motor enthusiasts who for the love of cars who are constantly looking for information about cars on the latest trends, questions, fixes, driving, tricks, and accessories.


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