It's a external switch (mines behind the front bumper corner). At your coil pack there is a big plug with 3 wires in it. One of these wires tells the computer that the engine is cranking when you turn the key. If you disrupt this signal the computer will not turn on the injectors. I spliced into this wire inside the plastic harness and ran the wires to the switch thru the inner fender totally out of sight.