I want to put a flipdown unit in my wife's Acadia using the dome light that has buttons for on/off. There are three wires one constant, ground, and a door ajar trip. I know I can tap into the constant for power but have read people having trouble with this killing the battery. I really want to be lazy and not rip apart her vehicle to accomplish this. Can I hook it up to this constant and put a snazzy toggle switch on the dvd unit (something that blends) to turn power to the dvd unit off when not in use to bypass this battery issue????