Abstract: A low tire pressure detector and magnetic signal sending unit includes a bellows charged to a reference pressure for moving a magnet from a shielded position to a signal emitting position when tire pressure operating outside the bellows decreases to a predetermined value. A latching force is established by the magnet to operate against the bellows force to help maintain the magnet in the shielded or non-signalling position. The magnitude of the latching force is controlled by a polepiece of thin cross section which saturates under the influence of the magnet to limit the latching force to a fixed value. The spring force of the bellows is sufficient in the absence of a pressure differential to overcome the latching force and move the magnet to signalling position. A ferrous slug mounted on the movable end of the bellows is magnetically coupled to the magnet assembly to form a releasable connection between the magnet assembly and the bellows.

Abstract: A circuit is provided for a tractor/trailer combination to provide a warning in the tractor of an event such as low tire pressure occurring at the trailer utilizing only conventional wiring connections between the tractor and trailer. When low tire pressure occurs, a flasher circuit on the trailer flashes the trailer marker lamps which are normally energized so that the flashing lamps are visible to the operator. The electrical pulses in the marker lamp circuits are sensed by a detector in the tractor to illuminate an indicator lamp in the tractor.

Abstract: A translucent indicator drum is rotatable to sequentially position messages representing events, which may occur at remote points in a vehicle, adjacent a viewing window. A rotary switch operated by the drum cooperates with a number of event sensors to energize a buzzer upon the occurrence of an event not represented by the message adjacent the viewing window and to energize a lamp when the drum is rotated to position the message representing the occurred event adjacent the viewing window.