Glow Plug System

The glow plug system is designed to provide easy starting when the engine is cold. Under varying engine starting conditions, different levels of voltage are fed to the glow plugs (through the 2 relays and dropping resistor), heating the plugs sufficiently to ignite the fuel charge.

When the engine reaches normal operating temperature, the glow plugs are no longer necessary and all power to them is cut. If the ignition is left in the "RUN" position with the engine off for more than about 3 seconds, the first relay opens, cutting power to the plugs to prevent damage from overheating.

When the engine is cranked, the control module cycles on preglow relay No. 1 for 1-6 seconds. After the engine starts, alternator output signals the module to stop relay No. 1 and an afterglow function takes over.

If coolant temperature is below 86°F (30°C), afterglow relay No. 2 remains closed. This applies 6-6.7 volts to the glow plugs through the dropping resistor. When coolant temperature is above 86°F (30°C), the control module opens No. 2 relay, cutting off all current to glow plugs.