the switch shouldnt be live should earth
out shouldnt it

SENDER for gauge shud earth out yes, thats how u check ur gauge if its working, pull the plug off, earth it out on the engine and needle shud raise up.

thermo switch ,, may work the same way meaning it will you the earth for the fan motor thus fan motor shud have a permanent live feed then. usually work the other way round, thermo switch gives ur live feed to fan motor . like i said though cud be wrong