Troubleshooting Brake Controller Stops Working When Brake Magnets Touch Drum

Published 10/31/2019

Question:

Trailer brakes stopped working, i checked over every wire i could see and found nothing. i did find a bad magnet, replaced that and they worked/had green light on the dash everything was working. The second the magnet touchs the drum the light turns red and it says check trailer but if i Energize the brakes manually they work, but still says check trailer and wont Energize on there own. I know its not the controler because i have 2 other trailers and they work fine. Any idea on what it could be?

asked by: Tim

Expert Reply:

Sounds like you might have a short to your trailer frame. You might use a circuit tester like part # PTW2993 to test to see if there is voltage on the frame of the trailer due to a short by putting the positive probe on the frame and the ground probe to the ground pin of the trailer wiring on your truck. If you find that your frame is energized this would explain why the magnets touching the drums is causing an issue on your controller.

This scenario would be caused most likely by the 12 volt circuit of the trailer wiring shorting out to the frame via exposed or cut wire.

expert reply by: Jameson C