I installed a kill switch on my 85 Cutlass back in 97 when I was in Cherry Point. The only thing is, most people install a "kill switch" to open a circuit to disable something (spark, power, fuel pump, etc) but I actually wired mine from the power of the distributor cap to ground. So if this switch was left "closed" when you turn the key on it would blow the fuse. This way, even if the thief found the switch after looking for why the car wouldnt start, they couldnt just flip the switch so the car would start. They would flip it and they car would just crank and not start. You would have to go under the dash, replace the fuse with a spare fuse that you just happen to have on you (unlikely) and then hope the switch is in the right position so it wouldnt blow the fuse again! This thing worked so well that I blew a ton of fuses forgetting to turn the switch off! LOL.... But the car never got stolen (or broken into) so I never got a chance to test it (and catch a thief) but I did end up buying a ton of 15 amp fuses!
So if you do install a kill switch I would recommend to do it that way. Because if all the kill switch does is open a circuit, then you risk the thief finding the switch, flipping it and the car starting right up. Good luck yall!