I have a '96 Explorer.
There is an air nipple beside the licence plate on the rear bumper.
I can't find any reference to it in the manual or on this forum (or anywhere else using a Google search).
What the devil is that thing for?

 

did someone add air shocks ? .......... probably not factory install.

 

X2 crawl underneath and look around for hoses, maybe you do have air bags under there,if in good shape could be a bonus