alright people got one of these boost gauges off ebay because it was cheap

http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=290114613916

it has 3 wires coming off it

red - 12v ignition switch
black - earth obviously lol
orange - 12v lighting

were will be the best place to wire them up too will it be on the back of the headlight switch and if so does anybody know what colours i have to go in to