That link should explain it all
Your tac, if like mine should have 4 wires
Red-pos battery, under the dash in the kick panel- i wired it to accessory slot
White-light, i wired mine to my dash lights so it dims
Green-find the green wire on the coil, tap into it.
99WJ Laredo I6-A 2wd
88XJ-Building on a budget.
95 E34 540i-DD