Coolant Sensors on Coolant Flange

[Retrocool]

There are 3 on the coolant flange which connects to the front of the block, 2 top and 1 underneath. Its a 1.6 driver, EZ engine code.

What do they do?  and which one controls the coolant temperature gauge on the dials?

Everytime I start the car the gauge would lead me to believe that I'm seconds off exploding

Many thanks

[Santiago]

Reddish one on top = thermoswitch  for relay for manifold pre-heater
Grey one on top = thermoswitch for autochoke electrical heater
Black one underneath = gauge.