I just bought a 2003 LTE. The navigator is in need of a map update. Called Garmin said its out of date they can't do anything for it. I want to switch it out for a Garmin NUVI 40 that will be in a water proof case. I would like to remove all the wires from the old one and hook up the new power lead. The question is should I just hook up to the battery or try to hook up to the old power wire that would be controled with the key and not always be hot to the GPS unit.