water level indicator/warning

[pug306driver]

I am about to replace the thermostat for a new gates one which I will drill 2  3mm holes in the flange to aid bleeding/filling.

The car has a temp gauge and a sensor in the expansion tank, to warn of low water level??

what is the electrical test procedure for this water level sensor please.

If I empty the tank, so the sensor float ? goes down, what indication will the dash give me??

will it show a small red light??

thanks.