What is this un-used plug??

[Boiseflyfisher]

The write-up thread is "Compass and Thermometer" for anyone interested and a few others I believe.
http://www.toyota-4runner.org/3rd-g...hermometer.html?highlight=compass+thermometer

 

[paddlenbike]

thedurk--thanks for taking the time to post. That's something I will be looking into.