Troubleshooting Trailer Brake Lights Only Working Intermittently Using a Circuit Tester
Question:
The right rear trailer brake lights only work intermittently. We have checked all of the fuses. We have replaced the multi-function switch. We still have a problem. Help.
asked by: Angel C
Expert Reply:
This sounds like either a loose or broken connection, or a bad ground causing your trailer brake lights to not function properly.
First, test the vehicle side connector with the trailer detached. You will need to check the functions to make sure they are working properly. Using a circuit tester, like # PTW2993, test the connector for left turn and brake, running lights, and right turn and brake. If everything is working properly, move on to the trailer.
You will need to check the wire that carries the signal to the brake lights from the trailer connector, all the way back to the trailer lights. First, you will have to find the correct wire. Using a circuit tester, find the wire that only carries a signal when you step on the brakes. Once you find the wire, test it at various locations throughout its length to find if it is broken at any point. At the same time you can check to see if any connections on that wire are loose.
If the wiring is fine, you will need to check for a proper ground at the connector and at each taillight. The taillights are grounded through the mounting bolts. I have included a video that explains how to test for a proper ground. Basically, you will test wire the brake light wire that is supposed to be hot when you step on the brakes. If you cannot get a signal at the taillights you might have a bad ground and you will need to try grounding in a different location.
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Bob C.
9/8/2020
We are having a similar problem except that when the brake light is out the trailer brakes also stop working. Getting a message on the brake controller that the trailer is not connected. Truck dealer says controller is good. Trailer shop says trailer is good. Have replaced truck and trailer connectors. Still have a problem. Any thoughts?