A method to prevent unauthorized use and/or access to a vehicle is disclosed. The method includes apparatus which is positioned within a known motor housing and actuable only within the motor housing. In one embodiment, an ignition generator coil interrupt circuit is provided and mounted directly within the housing of the motor. A switch is connected to the circuit which allows power interruption to the ignition generator coil. When the switch is activated, power interruption of said ignition generator coil is achieved to disable the engine from normal operation. Conveniently, the interrupt circuit is positioned entirely within the housing and therefore inaccessible for tampering. In another embodiment a switch circuit is positioned between an ECM motherboard and sensors typically associate with an automobile engine. This circuit is useful for arrangements which do not include a magneto/stator arrangement.