Engine switch ?
 

Hi there all, im new to this forum , i recently bought a cheap excel which i am in the process of repairing to use as a second runabout, first job was to replace bad starter motor, a bit fiddly but only one cut finger in process, whilst under car and looking at rear of engine i noticed a broken switch ! It screws into block and goes up and fits in a sliding bracket behind injector rail , has a plug with 3 wires
Wonder if anyone knows what its for ?? Thanks in advance !!,