Trailer wiring help

[airnathan]

I have an odd issue with my boat trailer, at least odd to me in that I just noticed it. When I have my car headlights on the trailer running lights work but the trailer brake and turn lights do not. When I have my car head lights off the trailer brake and turn lights do work. What would cause this? From what I can tell the wires them selves are fine, no mismatched colors. I have tried it on a couple other cars and same issue so definitely a problem with the trailer wiring. Any help or suggestions would be appreciated.

[jpollman]

Check your grounds!

Sounds like a bad ground on the trailer to me. A bad ground can cause all kinds of freaky situations. A good rule of thumb is that whenever you have something strange happening with your trailer lights, the FIRST think you should do is make sure that you have a good ground. Many times that will solve the problem.

John

[paulywood]

Yep, what he said. Usually it's a ground problem.

[Quaaack]

As mentioned above sounds like a weak ground.