Recently the water temperature gauge in my 1993 FD stopped working. I've replaced both the gauge and the sender so the problem appears to be a electrical one.

I know that the water temperature sensor output is sent to the ECU (pin 3e) but I'm not sure how the data is processed. I'm also not sure if my ECU is actually receiving the water temperature, or if the problem is somewhere else in the harness. Diagnosing issues like this is beyond my expertise and ability.

The car runs fine, and I haven't noticed anything operating outside of normal parameters.

My question is this: is it dangerous (for the engine) to continue operating like this? Does the ECU use water temperature to adjust the richness of the mixture? I plan on buying an Apexi ECU in the near future, so I don't want to spend money fixing the original ECU as long as I'm not hurting the engine.

If this is bad for the car, how hard is it to diagnose and repair issues with the wiring harness?