installing an alternator

With a one wire alt if that one wire is on the vehicle side of the switch then turning off the switch only separates the battery. If the alt is working then it will keep working (I'm going to ignore how hard that is on the alt, and it is) and the engine will continue to run and all electrical in the car will continue to be live. So turning off the kill switch won't kill the engine or anything else so long as the alternator is producing.

If not a one wire alt, then using one of the multi-contact kill switches can be used to kill the alt's exciter circuit and it won't matter where the charge wire is connected.

I just ran into this. I had been planning on putting the kill switch on a drag car that I'm wiring for a friend in the ground cable. Thinking it thru that won't work because it doesn't also separate the alt's ground from the rest of the car, so if the alt were producing turning off the kill switch wouldn't stop the engine and everything else would still be live due to the alt's putting out power.