Glow plug control circuit

The glow plug control circuit (28) is coupled by lead wire conductors to one or more glow plugs (31-38) for energizing same and includes a resistance bridge, the resistance (30) of the parallel connection of the one or more glow plugs plus the resistance (76) of the lead wire conductors being coupled to the bridge which has a first resistance leg, a second resistance leg, a third resistance leg (53), and a fourth resistance leg (54). A junction (128,130) between two resistance legs (56,53) is coupled to a source of voltage potential and a junction (67) between the other two resistance legs (53,54) being coupled to a common or ground (67). A comparator (72) having plus and minus inputs (70,74) and an output (82) is coupled to the bridge. One junction (58) between two of the resistance legs (53,54) connected between the voltage source and ground defines a reference voltage and is coupled to the minus input (74). One of the other resistance legs coupled between the voltage source and ground includes two series connector resistors (51,52) which define a voltage divider (41) and which are coupled to the glow plugs. The junction (60) between the resistors (51,52) is connected to the plus input (70) and has a voltage which is a percentage of the voltage across the glow plugs so that less than glow plug voltage is supplied to the comparator (72) and so that when the plugs (30) are heated to a set temperature, the voltage supplied from the divider (41) to the plus input (70) is equal to the voltage at said minus input.