Yes, I just wired up a Brake Controller on my buddies '14 Tahoe. Went through the same ordeal. Wired everything under the dash, tapped and loom, secured I to place and turned the ignition key to get... Nothing. Heart sank, then I thought about it and got on line. For anyone else looking at this, you'll need a 8x1.25mm nut and a 6x1.00mm nut if you want power for both the brake controller and auxiliary in the 7 Round. One wire is tucked down beneath the brake booster (coiled and tapped to the loom) the other is between the fender and power distribution center(coiled and tapped as well).
I called the local Chevy dealer to get the nuts for it, but after telling them I was adding this functionality to the vehicle and providing last 8 of the VIN and waiting 4 minutes on hold, he came back to say "so this didn't come with the vehicle and isn't listed" I confirmed his "discovery" (lol) and told him what size the nuts were and asked if he had any... He said they didn't so I just went to the hardware store. Save yourself the headache and just go there first (dealership is actually 5 minutes closer to me, so I thought I'd give em a shot, but lost far more than 5 minutes while being on the phone)
Oddly enough, the fuses were there on his truck. Good luck on your project!