Troubleshooting Trailer Wiring that Stops Working Properly When Headlights are Turned On

Question:

when trailer is hooked up everything is fine. the brake light, turn signal, and tail light works. turn the car headlights on and the left side trailer brake, stop, signal light do not work. everything else is ok. why?

asked by: Nick

Expert Reply:

Your main problem is an insufficient ground for the trailer wiring. Try improving the connection of the main ground wire of the trailer wiring harness. Make sure it is attached to a clean metal surface. Or you can run all of the trailer wires back to the main ground. This is actually the ideal solution. But you can also check the current grounds for the lights to make sure they are making a solid connection to a clean metal surface.

What you described is the classic insufficient ground scenario so finding a way to improve the grounds will fix the problem. The issue is that when your headlights are on the maximum amount of amperage draw is put on the setup which if there's an insufficient ground this would be when this would show up.

expert reply by: Jameson C