some decks require 5 volts which is how much voltage is going through the hand brake when it is on. Just supply it with 5 volts, or like ahab said you could just ground it depending on the deck.
on the newer pioneers u can hook up the lumination wire... when you crank your car you turn the headlights on 2 times and leave the parking light on and it bypass's that stupid g-shock sensor.. so it doesnt shut off if you go over 15 mph!
you hook it to a swith the parking brake wire on one side of the switch and ground on the other then you have to pulse the ground by turning the switch off then back on alot of tvs are going to the switch if they don't have gps