Dashboard coolant temperature gauge not working

Technical Area Engine, Transmission, Exhaust etc
1
  1. My model of MX-5 is: NB 1999 BP4W
  2. I’m based near: Slough
  3. I’m looking for technical help or recommendations on: The coolant temperature gauge in the dashboard is not working. I know it’s the gauge and not the sender because the car has a ME442 aftermarket ECU and I can watch the temperature change in the PC interface, also the cooling fan is going on and off at the correct temperature. Does anyone have any idea what could be wrong and, if the gauge is faulty, what is the possibility of replacing it - it looks like the dash is a single unit and not separate instruments.

Thanks

John