Applying Brakes Causes Taillights of Trailer Towed By 2001 GMC Sierra to Malfunction

Question:

I removed a round six pin trailer wiring connection and installed a 4 pin flat: dark green to dark green, Yellow to yellow, brown to brown and white to white but when I put the brakes on the trailer tail lights go out. The trailer works fine with my 2002 GMC sierra but will not work on my 2001. All fuses are good. Any suggestions?

asked by: Leonard G

Expert Reply:

Things seem to work okay until you apply the vehicle brakes, is that correct? If so, it sounds like a poor ground connection. Make sure the white wire from your trailer connector grounds to the trailer frame (usually on the trailer tongue). Make sure this connection is secure and not corroded. Check the ground for each trailer lamp, as well. Each lamp should ground either through its mounting studs being in direct contact with the trailer frame, or by its own ground wire connected to the frame. Make sure all these connections are tight and not corroded, as well.

The design of the trailer itself might contribute to the problem. If the trailer features a tilting bed or a folding or tilting tongue, the point at which the tongue or the bed pivots might be a bit worn, and therefore not keeping a continuous ground connection. If this is the case, simply run a jumper wire from one side of the pivot to the other by using a length of wire with a ring terminal on each end to join the two sections of the trailer frame.

I'll link you to our trailer wiring troubleshooting article.

expert reply by: Mike L