2023 GMC Canyon AT4 Aux Switch

You’re not going to like the answer! you need “Accessory Wiring Junction Block Package – Part Number 84938257”, which is an underhood installation. It’s not cheap. I have one and I think it was around $500. It also takes connections for the “AUX 1-2-3” optional switch that you can buy and installs in the driver side bolster panel. If you’re not at least a little experienced with this kind of install then the dealer installation charge is in addition!

I should add that the wires for the AUX button already in the truck are behind the passenger side kick panel. The instructions are hard to find. I have them (mostly readable) for the power distribution box (Accessory Wiring Junction Block Package – Part Number 84938257) and the accessory with another 3 AUX switches (part number 84938261 – mostly readable). I can post them here if somebody will tell me how to do it.

I don’t know how to save to a google drive.

Also, the part number for the “Accessory wiring junction box is not correct. The part number above is included with part number 86544321

My truck is a 2023 AT4X but I believe that part number fits multiple trucks.

Under the hood on the passenger side firewall (about a foot to the right and just under the windshield a few inches) are two black bolts poking out with nothing on them. They are used to mount the box.

Sorry about all the posts but I keep thinking of things to include.

You can also call your dealership parts department (my dealer service department send me to parts for the instructions). Mine very nicely emailed the instructions.

Both part number 86544321 and 84938261 are shown and can be ordered on “accessories.gmc.com”. They are listed under the “electronics” section.

Instructions for hooking up the “Aux” switch already in the truck are included with the instructions for the junction box (86544321).

I posted the wrong part number for the “AUX1 AUX2 AUX3” optional switched too (sorry). The correct number is 84938259.

I think the part numbers are different for the Colorado and the Canyon. The numbers here are for the Canyon.

Ok, last update I promise.

The description for the three AUX switches box (84938259) doesn’t say that you need the junction box (86544321) but you do need it to install the optional switch box, even if you don’t use the AUX switch included with the truck.