Abstract: A device for preventing the theft of a motor vehicle employs a casing that encloses the vehicle's distributor in a virtually impenetrable shell. A stack of rotatable discs in the casing must be properly set in the manner of a combination lock to enable the high voltage electrical signals from the distributor to fire the spark plugs of the engine. The discs in the casing are set by dials within the passenger compartment of the vehicle. The discs have contacts on their surfaces which align when the discs are properly set to provide electrical paths from the distributor to electrical connectors outside the casing. The high voltage electrical ignition harness wires for the spark plugs are attached to those outside connectors. A cover is secured to the casing in a manner that enables the casing to be opened only when the discs are aligned in a pre-established relation, which can be different from the relation that enables the engine to be started.