The key to making this thing shut off the car is taking the output of the alternator and running it back to the battery, positive post. Gotta be a 8 or 10 gage wire, but unless you put the output of the alternator thru a relay, solenoid etcetera it will run on when you shut off your switch. Now, I would also put a big fuse or marine circuit breaker on that line in case it gets shorted (DAMHIK). Good luck!