When I wired the controller on a Pontiac it was a matter of finding which wire had power when the brake was pushed. It was helpfull to have a wiring diagram showing wire colors, etc. and how the brake circuit functioned. It's unfortunate provisions aren't there for a brake controller, especially if you have the trailering option. My 07 has a rated towing capacity of 4200 lbs which would required a controller if I were to tow with it.
I haven't installed a controller but about a year ago, thinking I might, I got a wiring diagram, possibly from the local library, showing the brake control wiring. Here's a link that might be helpful. I think it was an 05 MY diagram but should be close.
