Why Would Trailer Lights Stop Working When Headlights of Vehicle are Turned On

Question:

I have got a small trailer. When I have no lights on left and right blinkers work. When I push the break peddle it works. When I turn the lights on and turn the left blinker on the right break light flashers.

asked by: Steve Z

Expert Reply:

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.

expert reply by: Jameson C