Abstract: A warning circuit generates warning signals in response to a blown fuse in a vehicle brake system which includes primary and ignition-switch controlled. The back-up pump is driven by an electric motor. Control circuitry monitors and controls the brake system and the fuse protects the control circuitry from ground fault conditions. The warning circuit includes a warning lamp which is connected to the battery via the ignition switch and which is grounded through a transistor switch. The transistor switch is resistively coupled to ground and to the vehicle battery through the fuse so that the transistor switch becomes conducting to actuate the lamp upon the blowing of the fuse. Alternatively, a similar transistor switch may be connected to the output of an astable multivibrator, which in turn is connected to the battery via the fuse and whose output is inhibited unless the fuse blows while the ignition switch is closed.

Abstract: A warning circuit generates warning signals in response to conditions of a vehicle brake system which includes main and back-up brake fluid pumps. The main pump is engine-driven and ignition-switch controlled. The back-up pump is relay actuated and battery powered. A sensor switch opens upon operation of the main pump and a brake switch closes during an operator brake application. The warning circuit includes a first OR gate with inputs coupled to the ignition and brake switches. The output of the first OR gate is coupled to the relay and to a first warning lamp. The output of the first OR gate is capacitively coupled to the set input of a set-reset flip-flop and is coupled to the reset input of the flip-flop. The reset input is also coupled to a terminal of the back-up source. The Q output of the flip-flop is coupled to an input of a second OR gate through an inverter.