Abstract: An ignition disabling anti-theft device (16) for a motor vehicle in which circuit switching devices (18 and 20) are used to disable the ignition system (6) of a vehicle every time the vehicle engine is shut off. The ignition sysem (6) can be enabled only by the application of battery voltage from a pre-existing vehicle electrical circuit through a secret switch (10). Further, the anti-theft device only disables the RUN circuit to the vehicle ignition system allowing the engine starter circuit to operate and the engine to start normally either with an unauthorized key or by splicing wires in the ignition circuit. When the starter circuit is deactivated after engine start, the engine will die, simulating an out of tune engine. A bypass switch (8) is provided to allow normal, unprotected operation of the engine ignition system when required.