Automatic headlight control system

Claim 1

Apparatus for causing an external light system of a motor vehicle to be actuated when the vehicle engine is running, said vehicle having an electrical battery associated with the engine, and the running of the engine causing an AC signal to appear with a DC component at a terminal of the battery, said apparatus comprising an electrical circuit including: connecting means connectible to a terminal of the battery to pick up the AC signal and DC component, means for filtering the DC component from the AC signal picked up by the connecting means at the battery terminal to provide a filtered AC signal indicating an engine running condition, means for amplifying the filtered AC signal, comparing means for comparing the amplified filtered AC signal or other engine running signal obtained from the amplified filtered AC signal with a predetermined value and providing an actuating signal when the engine running signal is above a first predetermined value and cease to provide the actuating signal when the engine running signal falls below a second predetermined value lower than the first predetermined value, and actuating means responsive to receipt of the actuating signal to cause the external light system of the vehicle to be turned on.