Troubleshooting Brake Controller Install of 2014 GMC Sierra 1500 That Only Works with Override

Question:

What is the wiring diagram for 2014 Sierra to install brake controller. I installed it matching the colors but the brakes only work on manual.

asked by: Andy

Expert Reply:

We see this type of issue with GM trucks like yours pretty frequently with brake controllers. The issue is actually that you have a blown third brake light fuse in your truck. This circuit is also the same one as the circuit that tells the brake controller you are pressing the brakes so when it goes out the controller never knows you are pressing the pedal. An easy way to check this is to see if your third brake light comes on when you press the brakes.

expert reply by: Jameson C