Troubleshooting Why Trailer Lights Go Out When You Hit the Brakes

Question:

Im hooking up a 7 pin plug to the trailer lights. The lights have a yellow wire green and two browns. Everything works except when you hit the brakes the lights go out. Any suggestions.

asked by: Andrew

Expert Reply:

It sounds to me like you may have a ground problem. There are several places to look for a poor ground connection. I recommend starting with the trailer connector on the trailer. Check to make sure that the ground wire is secured to a clean metal surface on the trailer. In addition, each lamp/signal will also need to be grounded. Typically the lamp/signal is grounded through the mounting bolts having direct contact with the trailer frame.

If the area that the lights are mounted to is not a good source of ground, you will need to run a separate wire from each light to a clean, corrosion free, metal surface of the trailer to obtain your ground. This extra wire should be attached to the mounting bolt or screw that is connected to the lights internal grounding tab.

Next, I would take a look at the connector on the vehicle. You will want to check to make sure that it is free of dirt and corrosion and that this ground wire is also secured to a clean metal surface on either the vehicle frame or chassis.

If you find that all of the grounds check out to be fine and the lights on your trailer still aren't functioning properly, please feel free to email me and I would be happy to provide you with additional suggestions to try and locate the issue.

I have also attached a help article which covers ground issues that you may want to take a look at.

expert reply by: Leah S