Lamp failure warning system for road vehicles

Claim 1

A lamp failure warning system for a road vehicle including a source of potential; a first winding having first and second magnetically opposing coils, one end of each coil being connected to a common point; first and second lamps the failure of which is being monitored, said lamps being connected to the respective other ends of the first and second coils; a switch having first and second positions, said second position connecting the source of potential to the common point of the first winding to energize and light the first and second lamps; switching means responsive to magnetic unbalance between the first and second coils due to failure of one of the lamps; a warning light connected through the switching means to the source of potential, said warning light being energized when the switching means is activated due to said magnetic unbalance; said switch in the first position connecting said source of potential through a resistance and a first and a second unidirectional means respectively to said common point and said warning light; said warning light having a higher resistance than the first and second lamps whereby when the switch is in the first position current passes through the resistance and the first unidirectional means without illuminating the lamps, but if both lamps have failed, then current passes through the second unidirectional means to energize the warning light.