I have a 160hp p-pumped 6bt out of a delivery truck(no cpl plate) with a 3 wire sensor in the left rear of the cyl head. My question is what's it for? Eng is equipped with an electric fan clutch. Could it be the thermo switch for it? and if so how does it get wired?

 

water temp sensor

 

Why would it also have one by the upper water neck?

 

Probably for the electric fan. I installed a Horton electric fan and the sensor went to the left rear of the head,as you described.

 

You wouldn't happen to know how it wires in would you?

 

If memory serves me, I believe one wire is ground,one is power, the third goes to a relay for the fan. I am in Arizona and my truck is up home, so I am unable to verify.