I found what looks like a sensor hanging off a wire near the passenger side of the engine block. The engine is a 5.0L in a 1988 firebird.

Sorry for the bad cell pic. The sensor is in the middle of the pic...

Knock sensor?

 

Knock sensor or thermal switch for the fan. Since the thermal switch in the pic is clearly broken, id wager its that

 

Looks like its the temp sensor as her temp guage does not work.

 

The gauge sender is in the drivers cyl head

The thermal switch triggers the fan relay under most driving. Switching on the AC overrides this. Check the wire color, dk grn/wht or gry is thermal switch. Dk blu is knock sensor

 

The wire looks black only but it could be because its old. I think it is the thermal fan switch. Its in the same bundle that the starter wires are in. I'm going to replace the melted wire and broken connector and will report back.