It all depends on where your battery is located in your truck. Mine was under the passenger seat in a ROW truck (right hand drive), and I wired it to the battery directly, and fed the headlamps from the same side.
I bought a "project box" from Radio Shack to house the relays and add a little protection from the elements, and mounted the box to the top of the fender well under the hood.
Thank you - Samer
1996 Range Rover P38
Defenderless for now!