Club 80-90 Forums

Hi this is my first post for quite a while. I now have a 1990 1.6TD
I have a problem. The glow plug light is staying on for the full minute and a half regardless of temperature. I have read the wiki and studied the glow plug circuit diagram on there. But I still have a question. I have found all my temperature sensors. The coolant temperature gauge and auxiliary coolant pump sensors are on the hose at the top of the engine. The coloured wires are all correct and when I short them out they function properly. I believe my glow plug sensor is in the head at the back of the engine (drivers side) but it doesn’t seem right. It is a large screw in sensor with a single male spade connector. It has a single blue wire going to it. The central connector is permanently connected to earth regardless of whether the engine is hot or cold. If I disconnect the wire or short it to earth it makes no difference to the duration the glow plug light comes on for. I haven’t found a sensor like this on any of the supplier’s websites. It is way bigger than the M10 screw in sensors sold as replacements for VW part.
Can anyone tell me what this sensor is and how I should progress with my fault finding? I think I may have a problem with both the sensor and the glow plug relay.

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Oil pressure!!!! That's why it has no effect on glow plug on duration.
TD engines normally have 3 sensors, 2 in the coolant flange beneath the oil sensor, 1 in the coolant flange from the side of the head.

Oldbutgoodie you are a star!. I found my glow plug sensor hidden under the one I was looking at. It has the correct blue/white with brown wires and guess what? The brown wire was broken and not connected to the sensor. I'll be able to sort this. Once I've nailed this I'll come back with my intermittent buzzer of doom problem.