Light control apparatus for a vehicle

In light control apparatus integrated with a vehicle headlamp driving system using headlamp driving relays, a light sensor, a lighting switch which selects between a manual mode or an automatic mode of operation, and a control unit having power supply and power ground terminals, light sensor terminals connected to said light sensor and operation mode terminals connected to said lighting switch and said relays, which unit controls the driving system relays in accordance with an output of the light sensor when the lighting switch selects the automatic mode for driving the headlamps;

• the improvement comprising;
• two power source systems associated with said control unit and including two power supply lines connected to corresponding power supply terminals and two ground lines connected to corresponding ground terminals of said control unit, and
• two headlamp driving systems associated with the headlamps and connected to corresponding headlamp operation mode terminals of said control unit, wherein each headlamp driving system is arranged to apply a drive voltage to a common pair of headlamps,
• said control unit including microcomputer means and means for detecting signal levels at at least one set of said power supply terminals and said headlamp operation mode terminals of the control unit, and for coupling the detected levels to the microcomputer means,
• wherein said microcomputer means includes means for judging the existence of a fault condition according to a difference between signal levels detected at said at least one set of terminals, and
• an alarm indication system including a lamp or buzzer coupled to a warning terminal of said control unit for indicating a trouble condition in response to operation of said signal level detecting means and the judging means of said microcomputer means.