Troubleshooting No Power on Trailer Brake Controller Black Wire

Updated 04/09/2019 | Published 04/07/2019

Products Featured in This Question

7- and 4-Pole Trailer Connector Socket w/ Mounting Bracket - Vehicle End

(2712)

$45.84

Pollak Circuit Breaker - Cycling/Automatic Reset - 30 Amp - Straight Mount Bracket

(74)

$5.42

Question:

Trailer brakes suddenly stopped working and have no power on the electric brakes. We tested the red and black wires that attached to the box like your article suggested. The red one gets power when the brakes are depressed, but the black wire gets no power. Where do we look to see where the power comes from and how would we fix that? Thank you.

asked by: Stacie Z

Expert Reply:

Not getting any power on the black wire is usually caused by something simple like a blown fuse under the hood. I'm not sure what vehicle you have but if it features a factory tow package this is most likely the culprit. Check your owner's manual for the fuse locations and find the one related to the trailer brake controller. Check this fuse and replace if needed.

The black wire coming from the brake controller carries the 12V circuit to actually power the unit. Basically if you aren't getting any power on this wire then the brake controller itself is not on (which is why the brakes aren't working). The red wire is its brake input circuit, which is what sends power from the brake pedal to the controller. Since this circuit is before the controller, it makes sense that you're still getting appropriate power there with the brake pedal depressed.

The blue wire coming from the controller is the brake output to the 7-Way. With the brake controller shut off you would not be getting any power here either.

Otherwise the black wire should be run under the hood and connected to the battery via a 30 amp breaker like # PK54530. You can check there to make sure everything is still secure and connected appropriately.

If this does not resolve the issue please let me know and we can continue to troubleshoot.

expert reply by: Chris R