pop the cover off the fuse box and find the two studs for aux power and trailer brakes. you'll need to put the fuses in the appropriate location too. the wires should be labeled and tucked between the fuse box and fender if they are not already landed on the studs
Stud #1 is a 40 amp cartridge style fuse which feeds the +12v wire in the 7 way trailer connector. Wasn't populated from the factory on mine, but once plugged in, this is a direct connection to the battery.
Stud #2 is a 30 amp cartridge style fuse that feeds battery power to the relay block (interior, by the driver's left foot) where the brake controller harness plugs in. Supplies the +12v to the brake controller, which in turn provides electric brake power in the 7 way trailer connector.