Troubleshooting Trailer Lights That Stop Working When Vehicle Headlights are On

Question:

I put new lights and wiring on my galvanized boat trailer and everything works well, except when I turn on the headlights - then nothing works at all. No turn signals or brake lights. When the headlights are off everything is fine. I have a tester and the problem is not on the tow vehicle, all three grounds main and each light are fine. Thanks.

asked by: JonE

Expert Reply:

Your trailer taillights aren't sufficiently grounded. It sounds like your tail lights function until the additional load of having the head lights of your vehicle are turned on and then the lights cut out.

Most trailer lights ground through the mounting studs if they do not have a ground wire on them. In either case, you will need to make sure the grounds are connected to clean metal surfaces on the trailer frame.

The other ground to check is the one that runs from the trailer 4-way to the trailer frame. Make sure its connected to a clean metal surface.

I attached a couple FAQ articles that you should find helpful also.

expert reply by: Jameson C