Mystery Plug, wires and hole in dash

[MASTERBrian]

About a year ago I purchased a 2012 yukon xl denali from a local dealership. There is a small hole that is in the dash, odd location though, as it's on the lower corner and almost obstructed by the arm rest of door. The plug is a flat plug I'm told resembles a brake controller plug. I've tried tracing the wires, but haven't been able to figure out where they go. Under the hood are two? red wires that tie into the accessory bolts on front of fuse panel.

Now I'd go with the brake controller theory, especially after I just found this article.... https://www.etrailer.com/faq-tb-0007...e-Control.aspx
BUT, my Denali comes with a built in brake controller. So why would it be changed out? It still appears to function, though I haven't hooked a trailer to it to find out if works, but messing with the controls it brings up settings on dash. The last mystery wire, I was able to track goes all the way up under the rear of the bed and stops. It's been terminated to nothing. Haven't yet checked it for power or traced it back.

Inside the cargo area something was apparently bolted down and I'm thinking that wire may have provided power. The holes have since been plugged, very professionally I might add.

Trying to solve this puzzle. At one point I had located the previous owners, but everyone told me it would be creepy to contact them and ask.

A friend that has a motor home thought maybe they towed it behind a motor home and had a break controller inside the yukon to control it's brakes??!!

I'll try to get pics if it'll help.

[MASTERBrian]

Here's some pictures.

The hole in dash, looks like switch went there?

Then the plug that's tucked under dash.

Lastly two pics of the under hood panel with 3 red wires that seem aftermarket, but sort of disappear into harnesses.

[MASTERBrian]

The more I read, the more im convinced it was an aftermarket brake controller. I wonder why once would remove, they aren't that expensive, but I also wonder why install, unless the factory one is that bad.

I have no current use for controller, but guess I better check mine out to see If it works or not in car I decide I want to use.

Lastly, I haven't seen signs of how they'd have mounted to the dash, because they generally require two screw holes. I'll take a closer look for signs though. Maybe that used that lone home somehow or maybe it was a toggle for it...hmmm.

[Palf70Step]

There was factory wiring for a trailer brake controller. Normally it is just stuff under dash and you add the appropriate connector for your brake controller. You could just zip tie or tape that up under the dash like the factor did.

https://www.youtube.com/watch?v=nf9bHdmwf2M

[MASTERBrian]

Originally Posted by Palf70Step

There was factory wiring for a trailer brake controller. Normally it is just stuff under dash and you add the appropriate connector for your brake controller. You could just zip tie or tape that up under the dash like the factor did.

https://www.youtube.com/watch?v=nf9bHdmwf2M

I'll watch that youtube, but I found a few holes drilled in the HVAC vent that shoots air at drivers feet. I think that was were a brake controller was mounted. I still don't understand the need for an aftermarket controller when this truck came factory with one. I understand some will say they aren't as good and maybe that's the case.....I don't have enough experience with that, especially with this truck. A buddy has a 2015 3/4 ton pickup and he hauls a dump trailer with brakes and says his works great.

Hole in dash unexplained still, likely a toggle but for what....there's holes in the cargo area, that I think maybe they had a permanent mounted cooler, so maybe they had that on toggle. Those wires should be somewhere if so. That is still a guess at best.

[MASTERBrian]

That video definitely shows exactly the wires in question, minus the red wire with a bit of loom on it that also goes to that post. I have seen it in other pictures, so now I'm curious what it goes to.

Now I need to hook up to a trailer or find another way to test that my factory controller works and forget the rest for now. I'd like to clean up the way those wires look, but I'm just anal that way. I realize the entire thing seems anal probably, but I want to be certain no loose 12v wires running around my truck not hooked to anything. At least the puzzle is coming together. Thanks for the video.

[Palf70Step]

The factory did not have the actual controller, just the wires to the hitch area. That is what those wires are for. The individual had to add the controller. Can't explain the holes in you AC box/duct, but some black gorilla tape will seal that up.

[MASTERBrian]

Originally Posted by Palf70Step

The factory did not have the actual controller, just the wires to the hitch area. That is what those wires are for. The individual had to add the controller. Can't explain the holes in you AC box/duct, but some black gorilla tape will seal that up.

On certain trim levels they certainly did have a controller. There's a controller built into knee bolster. If you look at my picture of the knee bolster, part with hole drilled, you can see the factory controls molded in just towards the top of that pic.

The holes are where previous owner must have installed an aftermarket controller. Those instructions apparently hold true for adding an aftermarket controller in place of factory. The instructions I posted speak a bit about it....I just don't understand what they'd gain by going aftermarket over factory. My factory installed controller shows output gain and such on the In Dash Display.

My bad on saying the holes were in the duct, they are in a black plastic piece that the knee bolster screws into. On quick glance under it looked similar to duct in that it has a deflector of sorts molded in. No harm in them being there.

[95 S_Trucker]

Originally Posted by Palf70Step

The factory did not have the actual controller, just the wires to the hitch area. That is what those wires are for. The individual had to add the controller. Can't explain the holes in you AC box/duct, but some black gorilla tape will seal that up.

You can see the factory brake controller in the first pic the op posted:

[95 S_Trucker]

The factory brake controllers work really well. It uses the brake pedal position sensor as an input. Aftermarket brake controllers use weights or a timer(solid state controllers).

The factory brake controller on my 2011 works a ton better than my prodigy P3(the best aftermarket controller there is) that i have in my 99.

[Palf70Step]

Sorry I missed that, I had never seen a factory one before. Knew they prewired them for hitches and the controllers. Learn something new everyday.