Interrupting the coil, fuel, ignition is a bad idea. Stick with the starter. dangerous to have component failure at 55 and lose your brakes and steering. Happened to a friend (relay crapped out) and he took out a family because he couldnt stop in time. Luckily nobody was seriously hurt.
There is a reason that you can not but an alarm anymore with IGNITION KILL. Its all starter kill now.
