Looking for - air gauge "sensor" for air pressure - in the instrument panel.

No I forgot about it. I’ll do it next time it happens.

 

AND NOBODY ANSWERED THE QUESTION...........

 

To answer the question, it'll be on that pass-through posted above by socalxpress and it'll look like this:


There are several. One each for the two tank gauges . . .

The part number on there may be 20449988 or 20476992. Apparently Macks might have the part numbers 22443498 or 64MT475M. Dorman sells an aftermarket version with part no. 904-7510

They come in and out just like any quick-connect fitting. You would depress the collar, preferably with the Lisle 3/8" air-line-disconnect tool, and twist and yank. Recently I had to insert another tool in for prying leverage while leaving the Lisle tool in to keep the collar down.