for the JK owners...
http://jpfreek.com/2015/11/16/diy-je...k-kill-switch/
Even cooler is an RFID kill switch.
https://www.youtube.com/watch?v=AJCRBA547gU
A buddy puts'm on his vehicles.
He simply cuts into the Crankshaft Position Sensor circuit (a simple sensor) - easy to locate and keeps the motor from running w/o that critical part
I have one on my TJ that uses a magnetic switch, interrupts the ADE system.
You can also use the factory cigarette lighter as a kill switch if you remove the heating coil and use the ground leg to complete the circuit (push the lighter in to run the car... pull it out or remove it and the car wont go).
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~Not All Who Wander Are Lost~ (at least not all the time)
So symple to do really.
All you need to to interupt the ground of something important.
Like the crank sensor as fore mentioned.