im guessing ur question is where to tap into a 12 volt wire, that is only on when ur car is on? and turns off when ur car is off? u can tap right off the ignition wire of ur car, if u want u can then add a toggle switch if u like to turn it on and off, when u break into the wire harness underneath ur dash you will see one set of wires (about 4 wires in the particular sleeve) with a white wire with a black stripe, will be the biggest wire down there (some wires are the same size but none will be larger), u can tap directly into that one, and the power will only be turned on when ur key is turned to the on position. i think that answers ur question if not let me know.