Glow Plug System: Description and Operation

Fig. 1 Super-Quick start glow plug control system schematic:

This system, Fig. 1, is used to enable the engine to start quickly when the engine is cold. The system consists of four glow plugs, a control module, two relays, a glow plug resistor assembly, a coolant temperature switch and connecting wiring. Relay power and feedback circuits are protected by fusible links in the wiring harness. The control module is protected by a separate 10A fuse in the fuse panel assembly.
The super-quick start system eliminates the waiting time to start the engine. When the ignition switch is turned to the ON position, relay No. 1 also closes and full system voltage is applied to the glow plugs. If the ignition switch is left in the ON position approximately three seconds more without cranking, the control module opens relay No. 1 and current to the plugs stops, preventing overheating. Relay No. 2 does not close until the engine is cranked.
When the engine is cranked, the control module cycles relay No. 1 intermittently allowing the glow plug voltage to alternate between 6 and 12 volts during cranking and with the No. 2 relay closed. After the engine starts, the alternator output signals the control module to stop the No. 1 relay cycling and the after flow function takes place. If engine coolant temperature is below 86° F, the No. 2 relay remains closed. This applies reduced voltage (6---7.6 volts) to the glow plug resistor for approximately 30 seconds.