Thanks. That's what I thought originallly but I searched high and low and followed all of the hoses and there's definitely no sensor in any of them.

I know that a local garage repaired a coolant leak a while ago and I wonder if they actually replaced a genuine Ford (Mazda) hose with a generic one and didn't reconnect the sensor wiring. Having said that I couldn't see any disconnected electrical plugs anywhere . Maybe the mechanic from that local garage cut off the wiring sensor and taped the ends up somewhere under the plastic conduit of the wiring loom. My mum said something about him not being able to source the sensor and in future she'd have to just listen out for overheating noises rather than using the dashboard gauge but I don't know exactly what was done or said and neither my mum or the mecahnic in question will likely remember now.

If I could find the sensor wiring I could probably fabricate something to house a sensor - a short circuit gives a full scale deflection on the gauge and an open circuit gives a cold reading on the gauge so it is a simple negative temperature coefficient device like a thermistor. I might drop into my local Mazda dealer and see if their system shows a cooling pipe with integral sensor.

If anyone does have a wiring diagram it would be really useful. I watched a video of some Dutch guy on Youtube fixing a similar problem and he mentioned that the temperature signal goes into the 7th pin (from the bottom) of the multi-plug connector on the back fo the instrument binnacle. If only I knew where the other end of that cable went I could probably fix this thing. I don't want her driving around without a proper temperature gauge really since its an old car and a lot of hoses etc. will be perished.

Thanks again