The most popular and cost effective way that I do for our customers is with a 12v spdt realy break open a starter wire and use a factory device (ie rear defrost button, push in cigarette lighter, install hidden switch etc) to imobilize the vehicle when it is not running. Now the key to doing this effectively, is to hide the relay out of sight under the dash, and making all your wire connections look stock, looming and running your wires with the factory wires. Now the reason for using a relay is because you dont want to use a switch directly to break open wires, (most of them melt, burn and short out) and a relay can handle 30/40 amps of current depending on what you get. If you or anyone has question on how to wire anything 12v to yuor vehicle, just pm me or let me know on here, as I am a certified MECP installer, and have been doing this for over 4 years
