yes 3x elements..
1x sensor (single wire) goes to your dash to show a useless needle
1x sensor (dual wire) resistance base, goes to your ECU to report back coolant temperature, this is also used to determine the enrichment values when the motor is cold.
thermostat aids the car to get to the right operating temperature fast, R34 GT-t like to operate around 90 degrees, R33 GTS-t like to operate around 80 degrees - I once bought a R34 GT-t thermostat and installed it into my car.. worst move ever LOL.. now I run the correct one.
The faster the car warms up, the less fuel it will used (based on coolant enrichment).
In your PowerFC menu.. there's a table that shows you water temp vs. injection correction - this defines how much additional fuel is required in vacuum and 100kPa+.. column one will have a lower valve than column 2 naturally.