Trailer Lights Not Working When the Headlights are Turned On in a 2003 Toyota Camry

Question:

Toyota Camry 2003, when our headlights are on, the running lights and brake lights and turn signals do not work on our trailer. When we turn off the headlights the brake and turn signals work but not the running lights. All we did was plug in the wiring harness no splicing, could the harness be bad?

asked by: Eron G

Expert Reply:

It sounds like you have a ground issue. When the headlights are on, the highest amperage draw is placed on the wiring system and, a faulty ground will show at this time. Make sure you have good metal to metal contact. Paint and corrosion can act as insulators, so make sure the grounds are touching clean metal. I would check all of the ground connections on the trailer.

First, check the ground at the trailer tongue. Take the ground loose and clean the connection point on the trailer and the wire end. Next, check the trailers tail lights. Most tail lights are grounded through the mounting bolts to the trailer frame. Make sure the bolt connections are clean and solid. If your trailer lights are grounded by a separate ground wire make sure that wire is attached to a good, clean ground.

Finally, check the ground on your Toyota Camry. Trace the white ground wire from the vehicles wiring harness and make sure it has good, clean metal contact with the vehicles frame. Again, check for corrosion and clean it up if you find some.

I am including a link to a FAQ page on trailer wiring. It will describe how to troubleshoot your trailer wiring.

expert reply by: Jeff D