Troubleshooting Trailer Lighting that Stops Working When Headlights are On

Question:

Put new trailer lights on lawn trailer. Both lights have direct grounds to vehicle hook up, as well as all other wires. Flashers, turn signals, brake lights all work fine. The problem is when the head lights are turned on the left tail light lights but the right tail light will not not light.

asked by: Phil

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