What does it do?
I have the 86 factory manual, and from that I've determined that it's an on/off temp switch in the thermostat outlet housing that goes to the ECU and only exists in 4WD models. (no determination of only manual transmission (I have manual, so it exist with manual) or both auto and manual)
Other than that, there's no testing procedures for it, and whether the switch is closed hot or cold.
Looks like it tells the ECU that the thermostat has opened up by either turning on or off........ (and only for 4wd models)
What would the ECU use this information for ?
Just curious......