Yeah its also for the emergency flashers that are supposed to work even with the key off. Still, it shouldn't use power with everything off. There is some parasitic draw from the ECU and dash with the settings memory, clock and some other stuff. Shouldn't be more then maybe 200miliamps though...enough to take a battery down in say 4 weeks or so. If its much faster and you are sure the battery is good, look to things like the winch controller that might have gotten water inside or starter solenoid..even the ignition switch.