Abstract: A security system for motor vehicles enables the ignition switch to be turned to the "off" position and the key to be removed without turning off the engine and accessories. Normal driving operation is restored by reinserting the key, turning the ignition switch to the "on" position, and preparing the vehicle for driving. If a person without the ignition key attempts to drive the vehicle, the engine turns off. The security system includes a solenoid, a switch means to energize and deenergize the solenoid, an ignition bypass line and switch, and a starter-override switch which prevents the flow of current to the starter should the ignition switch be inadvertently turned past the "on" position to the"start" position.