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How to Wire a Tail Light on a Semi Trailer

How to Wire a Tail Light on a Semi Trailer

May 13, 2020

Thousands of semi-trailers are used every day to transport important cargo all over the world. These commercial vehicles are used to move food, electronics, cars and other goods from distributing centers to local stores where they can be purchased by consumers. For these semi-trailers to be used safely they need to have tail lights that function correctly, keeping them as well as other vehicles on the road safe. In order to have tail lights that function well, it is important to know how to wire them so that they are able to illuminate correctly during braking.



Tools You'll Need:


Wire cutter


Step 1

Disconnect the wires from the old brake light. Some brake lights have a tab that can be pushed in with a thin screwdriver to release the wires. If not, you can use the wire cutters to cut the wires but make sure to leave enough length to connect the wires to the new light.

Step 2

Remove the old light by removing the bolts that hold it onto the trailer then pulling it off of the trailer.

Step 3

Place the new tail light onto the semi-trailer then bolt it into place with the supplied bolts.

Step 4

Strip each of the wires that you disconnected or cut in Step 1 so that about 3/8ths of an inch of wire is exposed.

Step 5

Twist the exposed ends of the wires then push them into the marked holes on the appropriate new tail light. On most models the driver side light will be connected to the brown and yellow wires while the passenger side will be connected to the brown and green wires.


Step 6

Pull on the wires gently to make sure they are securely in place. If they come out, you may need to strip off a little bit more wire then push them further into the hole so that they are seated correctly.


Make sure to disconnect the semi-trailer from any power source before working on any wiring. To disconnect the power source simply disconnect the wiring plug from the tow vehicle.

Some models of semi-trailers may use a different wiring scheme; though the wiring scheme above is true for the vast majority of trailers, make sure to check with the wiring diagram of your trailer to make sure that the correct wires are being used.