I scotchlockedthe towbarwires directly behind the rear lights and ran the wiring down through the bumper (as in the youtubevideo). I used some zip ties to make sure the weight of the wires didn't pull on the locks. It's not the ideal solution but has been fine so far (six months).
It wasn't too hard working out which wire did what by looking at where they connected with the bulb fittings. Earth was easy to spot as all wires were spliced off one wire. I did use a volt meter at one point but that blew a fuse in the car, best to do everything with the battery removed and then hope you've done it correctly afterwards!
I also used a light board to check I'd got everything wired properly.
Don't forget you'll need the radio code when you disconnect the battery.
Hope that helps.
Don't be an idiot like me and somehow confuse offside and nearsidewhen installing, it wastes a lot of time! I just used a standard wiring kit with a buzzer.