Trailer Lights Go Out when Brakes are Applied

Updated 04/05/2010 | Published 04/04/2010

Question:

I have installed the plug and tow adapter to the passenger side plug under the mud flap and grounded it. I have lights and turn signals, but when I hit the breaks all the lights on the trailer go out. I have checked all the wiring and bulbs and cant seem to find an answer. Please Help! Thanks

asked by: Regan L

Expert Reply:

What you describe is a ground problem with the trailer wiring. Starting at the rear of the vehicle, confirm that the ground connection on the Plug and Tow Harness is securely fastened to bare metal. If there is undercoating, corrosion, or grime built up under where you attached the ground, you will not have a good connection. Next, examine the point on the trailer where the trailer connector ground wire attaches. This can usually be found on the trailer tongue. Make sure the wire is in good shape, and the connection is secure and not corroded. The next place to check is the light fixtures themselves. Most trailer lamps obtain their ground connection by the mounting studs used to fasten the lamp to the trailer frame. If this connection is corroded or not tight, it can cause problems.

If your trailer has a tilting bed or a tilting or swinging tongue, the pivots might be worn a bit and might not be keeping a continuous ground connection. Use a jumper wire to join the stationary portion of the trailer to the tilting or swinging part.

You should find the problem at one of these areas. We have some videos that demonstrate how to troubleshoot linked below. I've also linked you to some troubleshooting FAQ articles that I hope you'll find helpful.

expert reply by: Mike L