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Troubleshooting Brake Controller that Doesnt work With Brake Pedal of 2003 GMC 2500HD Sierra


I have a 2003 GMC 2500hd crew cab pickup that I installed a Curt Triflex controller on. I also installed a brand new brake pedal switch. I am not able to get power to the trailer brake when push the brake pedal. I do have power to the trailer brakes if I manually activate the brake controller switch. I have double and triple checked that the quick plug wiring is correct. C=Blue B=Black D=Red F=White. All of my trailer lights work properly. The truck is new to me. When I purchased the truck it had an alarm and remote start installed. The installation of the alarm and RS was very poor and causing excessive parasitic drain 90 milliamps so I carefully unistalled these add ons and cleaned up the wiring. Now my standby drain is only 20 milliamps. I dont know if somewhere in that process those add ons had tapped into a necessary wire to connect the brake pedal controller to the trailer brake wiring harness? There was a wire from those add ons spliced onto the white wire of the brake pedal controller plug. I disconnected that wire. I would be so appreciative if someone would be willing to call me if any of your expert techs have any idea of what I might have going on. Thank you.


Expert Reply:

This is a super common problem for GM trucks around the age of your 2003 GMC 2500HD Sierra. Check the third brake light fuse of the truck. This fuse blows very easily in your truck and when that circuit is dead it takes out the circuit needed to activate a brake controller with the brake pedal. An easy way to check this is to press the brake pedal and see if the brake light above the truck bed activates. If so, then this is the problem.

expert reply by:
Jameson C

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