Not sure which transfer case is in a 1/2 ton, but I replaced the vacuum switch (valve) on my 2500's NP241D. The switch is on top, and I could barely see it from underneath the truck on driver's side. It was a blind task, but wasn't difficult to get a wrench on it.

 

NP231 but setup exactly the same. You can for a socket over it. Can't remember the side but it's over 1"

 

The switches do fail, but, more often than not, its just a bad vacuum line. The metal lines that run along the frame like to rust out, so, you lose vacuum, and things don't work as advertised. If, however, the vacuum is NOT switching from red to black (or vice versa) when you move the t-case shift lever, that is indeed a bad switch.

 

ok so if I switch the shifter from 2H to 4H the vacuum should switch from one line to the other right? I’ll give that a try to help further diagnose.

little backstory:
a few weeks ago the OD unit housing cracked at the transfer case and my transfer case was literally sitting onmy crossmember and the front shaft was smacking around on the crossmember as I drove (I was only in my driveway and it happened for like 10ft) I replaced my OD unit and bolted everything back up and it was driving fine until this issue happened. I think I might have jacked up the internals in the transfer case and not noticed anything until this recent issue.

again, thank you for BOTH the help you saved me an overnight stay somewhere And my wife was happy I made it home!

 

Personally I would pull the vacuum switch, it's not too hard just need a big enough socket. Then press the ball with your finger and see if the vacuum changes. The ball should stick out about halfway. If it doesn't it's the switch, if it does it's in the transfer case.

 

okay then will do! Thanks again!