How to Troubleshoot Intermittent Malfunctioning Left Turn/Brake Signal on Trailer

Question:

I have a 2010 dodge 3500. The left brake light and left signal light doesn’t work. It turns off when pressing brake sometimes and turns after when I restart the engine. This is a serious problem on road. Please advise me what is best.

asked by: Ronal

Expert Reply:

Because it sounds like you're describing an intermittent issue, you're most likely dealing with a poor ground connection. It's lot likely the main trailer ground on the trailer tongue is the problem since it's only happening on one circuit, but it's worth checking to make sure the ground wire from the trailer connector is securely fastened and isn't corroded. The ground for the left turn/brake lamp is where you'll most likely find the problem. Trailer taillights either ground by their mounting studs being in direct contact with the trailer frame or via a separate ground wire attached to the trailer frame. Check the grounds for that lamp, and make sure everything is tightly fastened and clean.

I've also linked you to a trailer wiring troubleshooting article.

expert reply by: Mike L