Hi, does anyone know about 'coolant sensors' and fiestas that wont start?

My 1994 1.1 HCS fiesta wont start, i had the same problem about a year ago and it was fixed at a garage by replacing the coolant sensor (think thats what he called it). As its been running fine for 12 months I thought I'd check this sensor thing over, but the manual isnt that precise about where it is.

I know its under the inlet manifold but there is a lot of stuff back there, which is it?

Also appreciate any tips on how to check it, someone mentioned putting a resistor on it if its taking incorrect readings.

Any help greatly appreciated

on the inlet manifold its the one on the very bottom where all the pipes meet in the middle.