Troubleshooting Trailer Lights That All Go Off When Brake Pedal Is Pressed  

Question:

Expert Reply:

The problem you are having with your trailer lights sounds like a ground wire problem. The first thing I would check is the wires. Look for any place you have a loose ground or if there is corrosion or dirt present that would not give you sufficient ground. If you have a tilting trailer bed or tongue you will need to run a jumper wire from the tongue to the trailer bed to make sure you have a solid ground.

The next thing I would suggest to check is the harness you are using. You will want to use a circuit tester like part # PTW2993, and with the trailer unhooked, check all of the pins on the vehicle harness to make sure all of the functions are working properly. If they check out, then move on to the trailer and with the harness hooked up, use the circuit tester and check all of the wires at the back of the harness for power.

To prevent further issues, I recommend using dielectric grease like part # 11755, when working with electrical connections. This keeps dirt and moisture out of the connections and helps prevent corrosion.

I have attached a couple of helpful articles about trailer wiring and how to troubleshoot you can check out.

expert reply by: Jeffrey L

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