Gooseneck Trailer Lights Get Brighter on One Side and Marker Lights Come on with Brake Lights

Question:

I have a 7 pin gooseneck trailer. Recently the left side side marker, brake lights etc. have gotten brighter than the right. The side marker lights on the left side come on when the brakes are applied. Any ideas? I have checked all the grounds I could find. It does this with two different trucks, so I am fairly sure it is in the trailer wiring. The trailer is a 28 pj. Any suggestions would be appreciated. - Thank you.

asked by: Bruce B

Expert Reply:

Checking the grounds was a good place to start. I think that it still may be a ground issue. There are several things you can check to determine if it is a ground problem. I would start with the trailer side connector and check for any dirt or corrosion and clean it out. Dirt and corrosion could cause a bad connection or a short which would lead to undesired results.

Next, I would check the ground coming out of the back of the trailer connector. It should be connected to a clean and corrosion-free bare metal surface on the trailer frame. A bad ground here could cause the lights to not work, work intermittently, or other unwanted performance. You can also check to make sure the wiring is not broken or frayed.

Next, I would move on to checking the grounds at the lights themselves. Many trailer lights ground through the mounting studs unless there is a ground wire attached. Again, the grounds will need to be attached to a clean and corrosion free surface. While checking the grounds at each light, you can also checking for any loose or broken wires that may be causing the problem.

I have included links to some videos showing how to check for a proper ground that may also help.

expert reply by: Michael H