Glow Plug Harness
The wiring assembly that delivers electrical current to the glow plugs in a diesel engine.
The glow plug harness is a wiring assembly that distributes high-amperage electrical current from the glow plug controller or relay to the individual glow plugs in a diesel engine. Because glow plugs require significant power to heat the combustion chambers, the harness wires are thick and insulated to handle the current without overheating.
Due to its location on the hot cylinder head, the harness is subjected to extreme heat cycles, engine vibration, and oil exposure. Over time, the plastic connectors can become brittle and crack, and the internal wiring can corrode or break, leading to high electrical resistance.
A damaged glow plug harness can prevent one or more glow plugs from receiving power, causing hard starting in cold weather, rough running on startup, and white exhaust smoke. Diagnosing harness issues involves testing for voltage at each connector during the pre-heat cycle using a test light or digital multimeter.