Glow Plug is a device, just like a spark plug, used to aid starting an engine, in this case a diesel engine. The has a feedback line to the PCM to facilitate failure detection. The PCM operates the glow plug relay for max. 120 s at an engine coolant temperature below 32 °C. The glow plug is an electrically heated wire, the heat generated by the glow plugs is directed into the cylinders, and serves to warm the engine block immediately surrounding the cylinders.

The following schematic illustrates the Mazda BT-50 .

Mazda BT-50 Glow Plug Relay Schematic Wiring Diagram

1 From main relay
2 Glow plug relay
4 Glow indicator light (IC)
5 Glow plugs
6 Glow plug circuit fuse
7 From battery

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