The inertia shut-off switch assembly is used as an emergency disconnect in the unfortunate event of a crash. REVOLT Custom Electric Vehicles has used it in every car they've built, hooked to the main contactor to disrupt the circuit. This item, the inertia shut-off switch pigtail, is the pigtail that is used to wire the switch to the 12v circuit that controls the contactor. In order to set up properly, the pigtail and the switch both need to be installed.