Troubleshooting Trailer Brakes Not Working When All Other Trailer Functions Work Properly

Question:

I just put a curt hitch and curt powered light pigtail on my 2012 Jetta. Everything worked when I started out. Now the brake lights on the trailer do not work, although they work on the car. The other lights, tail, and blinkers. work just fine... but no brake lights. Ive checked the connections and everything seems to be in order. The ground is good. What do I do next?

asked by: Dan B

Expert Reply:

I suggest first disconnecting the plugs and reconnecting them because sometimes you will get all the functions except one and the issue is just the clip not being seated completely. If that isn't the solution, then using an incandescent circuit tester like the Circuit Tester # PTW2993 to test your brake signal wire when the trailer is not connected. In a typical four wire flat system, this will be the brown wire. Test it for signal at the vehicle. if it doesn't work there, check the wire for any damage and test where that signal enters the pigtail. Replace wires where needed or replace the powered pigtail. If you have power at the connection for your brake function, we have isolated the issue to the trailer. Run a separate wire directly from the connector to your brake light to check for function by bypassing the trailer's current wiring. If that works, you know you have a wiring issue and you will need to replace the brake wire on your trailer. If that doesn't work, your brake lights on your trailer must not be functioning correctly and will need to be replaced because you have already determined the ground wiring is good.

I've attached an article on troubleshooting 4 way wiring installations to help as well.

expert reply by: Jason S