It will not stop the engine when it's running. The battery can be removed from a car and it will continue to run on the alternator's supplied power. You can re-route the alternator charge wiring to the non switched side of the isolator so the battery and the isolator are both on the same side and the rest of the car is switched off. The only problem is that the alternator is still live when the battery is isolated. Alternatively purchase a double pole isolator with two sets of contacts. (two big terminals and two small terminals) the small ones are to kill a vital circuit like fuel pump.