right boys. your shopping list: (bought from halfords)
3 reels of wire. 17AMP, but rated at 210w @ 12v in black, red and blue - ?2.49 x 3
2 30AMP relays. Probably get them cheaper from RS or maplins, but from halfords - ?4.99 x 2
assorted heatshink (to do a proper job) - ?1.09
and whatever method you want to attach the live and earth wires.