It’s a latching relay. Pulse 12v on one circuit and the relay closes and the car has power, pulse 12v on the other circuit and the relay opens and kills power. No power draw from the relay when it is closed or open, only when changing its state.
You have a link, part no. etc? Or even post a photo? Any inertia switches (that is OEM) are "latched closed" and open a circuit. So that would require a relay (or transistor etc) to invert, etc not sure how you'd implement that. Same problem, "draw on shutoff" Adding more circuit adds to possible failure, and defeat the purpose.
