Mystery coolant sensor

My '91 4.0HO has a small coolant sensor on the top of the head directly above the #6 exhaust port. Can anyone tell me what its function is? My 97 4.0HO that I'm swapping in doesn't have the same sensor (not even a hole for it) and I need to know if it's just the temp sensor for the gauge or something else.
TIA
ASATxj

It's the gauge sensor...

Yup! I checked the specifics out with the folks at accurate power and I have a plan in place to solve the problem. Thanks!!