Troubleshooting Boat Trailer LIghts that Don't Function Properly when Headlights are On

Question:

My boat trailer lights work fine when my vehicle headlights are not on. As soon as I turn on my vehicle headlights the left brake/turn signal light gets brighter. As a result the left brake or left turn signal light does not work as it is already continuously burning bright. I am running a factory round 7-way from my 2009 GMC Sierra to a flat 4-way connector. This is a new issue for me as it has always worked fine before this. Any help you can give me would be appreciated. Thanks very much.

asked by: Brian R

Expert Reply:

Most likely the problem is an insufficient ground on the trailer's wiring. Anytime you get bizarre trailer lighting functions like what you described when the headlights are on the problem is almost exclusively that the trailer light grounds can't handle the additional load put on the wiring when the headlights are on.

Make sure that the trailer side connector are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by: Jameson C