Troubleshooting Trailer Wiring That Stops Working Normal When Headlights Come On

Published 10/25/2017

Question:

Hi. I recently bought a 4-pin connector for my GMC Jimmy only came with wires bundled and clipped to the frame, for aftermarket completion and low and behold the 4 pin connector that is on the trailer has 5 wires going out to the trailer lights. The sharedinch connector is the brown one the taillamps/brakes. Ok, heres the weird part... When my vehicles lights are off, everything works fine. Brakes come on, turn signals work correctly. But when I turn the lights on, everything gets screwy... The taillights come on, but when I press on the brakes, the brake lights on the trailer do not come on, and heres the really weird one...the turn signal makes the trailer lights wig-wag...they alternate flashing, one side to the other, one at a time! Bizarre. I have no idea why that is happening. Do you???

asked by: Paul S

Expert Reply:

It's actually a pretty simple solution to the problem you have. Your trailer's lighting system needs a better ground and everything will work well. When a trailer's wiring ground is weak it will do some strange things like what you described when the headlights are on.

Try improving the connection of the main ground wire of the trailer wiring harness. Make sure it is attached to a clean metal surface. Or you can run all of the trailer wires back to the main ground. This is actually the ideal solution. But you can also check the current grounds for the lights to make sure they are making a solid connection to a clean metal surface.

expert reply by: Jameson C