Old school kill switches for mags were real simple. Replace your button with a water proof toggle. and add an Eye Bolt about an inch to the "engine off" side. Put a loop in your lanyard and thread it through the eye bolt and over the toggle. Tie the lanyard to your jacket and go racin. Toggle away from eye bolt, motor on. Toggle toward eye bolt, motor off. Driver leaves the vicinity toggle gets pulled toward eye bolt, motor off. be sure you leave enough slack in the lanyard so it doesn't go motor off if you move a bit in the seat.