You should have two power cables on your head unit one will say battery, this is to be connected directly to te battery and there should be another one which says att this one should be connected to the ignition. The battery cable will only use a small amount of power when swiched off this will keep all your settings saved on the head unit. The att will operate the head unit when the ignition is swiched on and then more power will be drawn down the battery wire while the unit is in opperation