it might not be a fuel cutoff switch; instead, it might be a starter kill switch. the difference is that the fuel cutoff will require your button to be in the "on" position while the car is running. a closed circuit must be maintained if the car is to remain running.

the starter kill switch just needs to be pushed to start the car. after the car has started, you can release the button (to the "off" position) and the engine keeps running.

to me, the starter kill button is just as useful and less risky since you run absolutely no risk of your engine turning off while driving b/c of a faulty relay/button on your fuel cutoff circuit.