Cars, boats and RVs frequently use battery cut-off switches to prevent a slow power drain on their batteries when the vehicles are not in use. Cut-off switches physically sever the connection between a battery and the devices that run off of it. This keeps devices that may be left on or automatically switch on from draining a vehicle's battery, leaving it unable to start. Cut-off switches may also be used as an antitheft device, because a vehicle will not start unless the cut-off switch is on.
Locate your vehicle's battery and the negative wire, which is usually black. Disconnect the negative wire from the battery.
Select a flat surface to use as a mounting location for the cut-off switch. The location should be close enough to the battery that the negative wire can reach the location and then reach back to the battery. Place the switch against the surface and mark the mounting hole locations with a pencil.
Drill pilot holes in the surface. The holes should be slightly smaller than the screws that you will be using to mount the switch. Screw the switch into place.
Cut the positive wire so that there is enough wire to run from the battery, to the switch and then to the wire's original source. Strip the last 1/4 inch of insulation from the new ends of the wires.
Insert the exposed wire ends into the switch's terminals. Different switches use different types of terminals, but most have a screw that you need to tighten to secure the wire.