Troubleshooting Right Trailer Brake Light Not Functioning but All Other Lights Work

Question:

All the lights work on my truck and trailer except rht rear brake light on trailer.

asked by: chuck

Expert Reply:

This sounds like a ground problem. A loose, broken, or corroded ground connection can cause all sorts of unwanted performance for electric components including trailer taillights. I would start with checking for a proper ground at the taillight itself. Many times, trailer taillights ground through the mounting studs. Check for any corrosion and give them a good cleaning to get the best connection.

You will also want to check the ground at the front of the trailer for any dirt or corrosion. Finally, check to make sure the actual connectors on both the truck and trailer are clean and free of corrosion. A bad ground or dirty connections are the two most common causes of lights not functioning properly. I have included a couple of videos below on troubleshooting the ground wire that should help.

Also, if you are using Light # ST70RB that you have referenced, make sure you are also using # A45PB harness. On this harness, white is ground, black is taillight, and red is turn and brake.

expert reply by: Michael H