Troubleshooting Trailer Brakes That Lock Up When a Brake Controller Isn't Installed

Published 08/30/2014

Question:

Okay , so when I get in my truck I can hit the brakes and my controller will light up and then I can slide the lever over and get a reading . If I let go of the lever and will then come up .c. And then n.c and I can no longer get a reading . This is when there is no trailer , I havent had a trailer on it yet that needed the brakes . Before I got this controller if I hauled a trailer equipped with trailer brakes the wheels on the trailer would lock up 100 like the truck is sending a full 12 volts to the wheels. Any idea why ? Also the truck is a 2000 Chevy silverado z71

asked by: Ross R

Helpful Expert Reply:

Sounds like you have some corrosion in the 7-way on your tow vehicle. This is causing your brake light circuit to short out onto your brake output circuit and causing the trailer brakes to lock up.

This would also explain the weird readings you are getting with your brake controller when it's not hooked up to a trailer. Look for corrosion on the inside and outside of the connectors, or even cut or exposed wire that runs to the connector and fix as necessary.

I attached an FAQ article on brake controller troubleshooting for you to check out as well.

expert reply by: Jameson C