Ok so you've got your power and ground covered..the other one probably white is for the ligh(s) inside the tack some people wire the power and the light bulb wire together so that the light is always on when your vehicle is on or some wire them to the headlights..the other wire is probably green and is wired to your distributor.
hope this helps
Looking for a new VW? How about a used vehicle? We are Central Albertas #1 source for pre-owned vehicles
I will beat any deal on a new VW for beyonders
Gary Moe Volkswagen/Gary Moe Used Car Superstore!
Red Deer, AB