Right Side Brake Lights and Turn Signal Do Not Work on the Trailer

Question:

Left light works fine. Right light has running light only, no brake or turn signal.

asked by: Woody

Helpful Expert Reply:

It sounds like your problem may be limited to just one circuit - the wire that carries the right turn signal and brake light. To begin testing, I recommend checking the vehicle side and trailer side connectors for any signs of corrosion or damage and repair as needed.

If the connectors look fine, I would test the vehicle side trailer connector with a circuit tester, like part # PTW2993, to make sure the vehicle is sending power to the trailer (see video). I would test each pin as a helper activates the different taillight functions on the vehicle.

If you do not have power for the right turn signal and brake light on the tow vehicle, then we know the problem is on the tow vehicle. If you have a factory tow package, you likely have a blown fuse. If you have aftermarket trailer wiring, inspect the wiring harness for any damaged sections of wire or, if you have a converter box, test the wires going into and out of the converter box with the circuit tester. I have attached a help article that explains how to do this.

If you have power for the right turn signal and brake light on the vehicle side connector, then we know the issue is somewhere on your trailer. Starting at the trailer side connector, follow the wires back to the taillights looking for any sections that are pinched, frayed or damaged. It may be possible that there is a short on the right turn signal and brake light wire. Finding and fixing the short should solve your problem.

If you do not see any damage to the wire, another possibility could be a poor ground for the right side tail light. I recommend either relocating the tail light ground or running it back to the main trailer ground. You could also check the main trailer ground.

expert reply by: John H