Truck marker light

Claim 1

A marker light for trucks, semi-trailers and the like having electrical systems with either positive or negative ground comprising a base having means for mounting the same on a truck, a lens mounted on the base, lamp supporting means, means for mounting the lamp supporting means on the base, said lamp supporting means having first and second lamp sockets for receiving first and second incandescent lamps, a ground terminal adapted to be connected to the truck electrical system ground, a power terminal adapted to be connected to the live terminal of the truck electrical system, a first transistor, a second transistor, a full wave bridge rectifier having its input connected across said power and ground terminals and having its output connected in series through the base and emitter of said first transistor to the first lamp socket and the filament of its lamp and also having its output connected in series through the collector and emitter of said second transistor to the second lamp socket and the filament of its lamp, a connection from the collector of the first transistor to the base of the second transistor for biasing the second transistor off only while the first transistor is on and current is flowing through the first transistor as would be the case when the filament of the first lamp is unbroken, and a bias resistor connected to the base of the second transistor for biasing said second transistor on, the bias from said resistor being overcome by the bias from said first transistor when said first transistor is on and conducting current through the filament of the first lamp.