How To Install A Brake Controller On 2017 GMC 4500 Cutaway Box Truck

Question:

I have a 2017 GMC 4500 cutaway box truck I need to put a brake controller in. I found the factory harness under the dash but it has no power, upon further searching I found the slots for all the trailer related fuses in the fuse box not to be wired. Where can I hook into to get switched power and stop light signal for the brake controller? thank you.

asked by: Matt B

Expert Reply:

If you look under the dash of your 2017 GMC 4500 Cutaway there should be a wire bundle with white tape. You can probably find it to the left of the steering column. They may or may not be identified with a white label.

I did some research on your 2017 Cutaway and on page 209 the following description of the wires you need are:

Black: Ground
Red/White: Battery Feed
Dark Blue: Trailer Brake Signal
Light Blue: CHMSL/Stoplamp Supply Voltage

You can use a circuit tester like part # PTW2993 to test the wires for function. You should have constant power on the red wire with the White stripe. The light blue wire and Dark Blue wire should show power when the brake pedal is pressed.

If the vehicle is a cutaway with trailer provisions, a 15 amp fuse will be shared for both left/stop trailer turn and right/stop trailer turn signals. However, the cutaway lighting connector will have a 10-amp fuse for each signal.

You can hardwire a brake controller like part # 90195 in the following manner.

Truck Red/White to brake controller Black for 12 volt power
Truck Black to brake controller white for ground
Truck Light Blue/White to brake controller red for brake light signal
Truck Dark Blue to brake controller blue for brake output to trailer

I also attached a helpful article that explains how to hardwire a brake controller from scratch you can check out.