Troubleshooting Wiring When All Lights Work Except Brake Lights

Question:

The brake lights on my trailer do not work from my tow vehicle. The running lights, turn signals and emergency flashers all work fine. A voltage meter on the tow vehicle shows 13ish volts from yellow and green when I press the brakes. Forcing power to the trailer with a regulated power supply on green and yellow lights up the brakes. Do you have any idea what my problem might be?

asked by: Chris

Expert Reply:

You will need to check the stop light and/or CHMSL fuses in the towing vehicle. You may find that is causing the issue. You can then check to see if there are separate fuses or relays for the tow package wiring. You can check the owner's manual to find the locations of any fuses/relays.

If the fuses and relays all check out it may be a problem with the ground. You will want to make certain both the vehicle and trailer side ground wires are attached to clean bare metal surfaces. Also make sure that the connectors are clean and free of corrosion.

If that all checks out then you will want to check the ground wires are each light on the trailer.

I have attached a helpful article that explains how you can test the vehicle and trailer wiring.

expert reply by: Jeffrey L