my CRAZY... (well maybe not , but its implementation is) idea was as following.
the kill switch simultaneously kills power to both the fuel pump and DME relays, and disables the wire going to position 4 in the ignition.
the wiring would have to be VERY discreet and stock looking, hidden away in line with the stock wiring harness, and the switch would have to be in an uncommon location, perhaps under a piece of carpeting with a little plastic cover on it somewhere, or behind the brake pedal O_o
for YOUR application however, the starter position wire would probably be the best option, since its RIGHT THERE and all you need to do is splice a single wire, done.
That would only protect the car against someone who has the key and the car is off, you could wire a reverse momentary switch right next to it to disengage the run position wire and kill the car during a carjacking by hitting them both... the thief would have no idea wtf is going on.
Alusil, Dinan DME | ITG Air Filter | Eibach/Bilstein HD | 26/20 Swaybars | Iridium plugs | Depo/ProLumen HID | Optima batt. | no AC | Stoptech brake lines, Frozen rotors, brass bushings, Superblue