I would like to recommend another option.
Tap into the Factory Trailer Brake Plug. I think this is probably the cheapest and cleanest option.
In the same box below the dash next to the brake (as described above) there is either a plug (factory trailer brake) or an open spot ABOVE the pins mentioned in this thread. The plug or open spot has 4 pins. Ground, Power, Ignition, and Trailer Brake.
Option 1: Those with Factory Trailer Brake
Splice into the Accessory wire in this harness via vampire clamp or ...
Option 2: Those with OUT Factory Trailer Brake buy the pigtail from eTrailer, Part Number 3016 and cut off the end to splice into it. Or pick up a trailer brake and have both.
Here is a video showing the Trailer Brake install. This Trailer Brake needs the same power/Acc wire so its a perfect spot to tie in.
https://www.youtube.com/watch?v=RMLd8L7Rcnk
Just my two cents.. Cheap and Factory Look in the box.
Huck
You can buy a pigtail from etrailer for about $15-$20.