Abstract: An improved glow plug controller is disclosed. The glow plug controller includes an analog temperature sensor, circuitry for converting an analog temperature signal to digital form, a microprocessor for analyzing temperature and other operating parameters and for controlling glow plugs and monitoring indicators in accordance with algorithms defined in the microprocessor. The temperature and control signals from the microprocessor are converted to analog form and applied to actuate glow plugs and indicators in accordance with determinations made by the microprocessor. A specific embodiment includes a manual override for facilitating operation even if the microprocessor should fail. A false temperature input is provided so that a false temperature representation can be directly applied to the microprocessor for factory and service center testing of microprocessor operation. Glow plug operation is controlled by way of a relay and multiple, independently fused glow plug circuits.