I just put a tow hitch and wire harness from the dealer on my '07 Tacoma. They both came with directions from the dealer however the directions for the harness were a little less than adequate since the harness is a mass of wires with nothing labeled. I was expecting some little union or something but instead what I got looked like I was going to have to rewire the entire truck. No Fear though, I'll give you the info I was missing so you don't have to spend an hour or so visualizing how this octopus is going to fit.
1. start off by knowing that the little black box in the middle of the main set of wires is going to mount inside your left rear tail light box on the nice flat wall beside the bed.
2. there are 2 set's of wires with double end's. one has a long set of wire and the other is a short set of wires. The short set is the left tail light and the long set is the right tail light.
3. the seperate long wire with a plug on one end and a round connector w/fuse on the other is run from the battery to the left rear bottom of the truck. Basically just follow the brake lines and keep it secure with the wire ties.
4. now just follow the directions the dealer gives you and you'll be fine.
hope this helps someone...............