Quote:

why cant you just put the alternator wire on the side of the main kill switch going to the front of the car so that the alternator is killed when the switch is off?


Because although that would break the path between the battery and the alternator (thus stopping the alternator being hot when everything was switched off) it means that the alternator is directly wired to the rest of the vehicle wiring - so if you switch the disconnect with the engine running the alternator will still power everything and the engine won't cut out.....

EDIT - I need to refresh more often