Well we offer two kits... the cheaper option is a splitter, extension harness and upfitter.
The crème de la crème harness, made by LVJ, replaces the existing splitter at the lights, connects them to it's own harness and the entire thing is brought up to your enigne bay. From here there is a built in weatherproof relay (one that tops all others I have to say) that is triggered from your upfitters. There is a 2nd trigger that is done from the BCM harness reverse light wire itself. Which is by your passenger foot well. So you'll use a pass-through upfitter to get to this wire. From here there is a wire tap for the BCM wire (but it's done inside the cab instead of out at the elements).