I have a 07 Tahoe and found the 4 wires for the controller under the dash.
But under the hood I found two different red/black stripe wires taped. Where do they go and what are they for? The owners manual said there is two curcuits under the hood but not much details.

 

one of them is for the power for the brake controller, while the other for the battery tow charge at the 7way. Route both wires to the underhood fuse block. Located on the front side of the fusebox near the driver headlamp you will see two studs when you remove the fusebox cover. The studs are of different sizes so you can get them wrong.Connect the red/black to these studs.You will need to put a fuse on the tow charge line in the fuse box. You will also need nuts for the studs.