Abstract: A plurality of indicating circuits are coupled to monitor the operating parameters or conditions, such as, for example, oil pressure, temperature, fuel level, and speed, of an engine or the like, and such indicating circuits provide an indication of the first occurring fault or failed parameter capable of causing engine shut down. Optical isolators are used to facilitate coupling respective indicating circuits to conventional condition responsive switches, such as oil pressure and engine temperature switches, and in response to an analog input signal proportional to engine speed a speed detector provides a digital output signal indicative of whether the engine speed is above or below a predetermined level. Moreover, after one indicating circuit has indicated a fault, a disabling circuit disables the other indicating circuits from indicating subsequent faults, and an automatic reset circuit effectively over-rides the disabling circuit to reset each of the indicating circuits upon engine start-up.