Where does the vacuum line hook up, that goes from the front diff to the transfer case

On the transfercase end at the vacuum switch on top of the transfer case. On the front diff. end it goes to A vacuum pod that operates A cable that is attatched to the differential. Been a long time but I think pod was on the passenger side front (hard to see,possibly under some other component) follow cable back from diff. if you can't see it.

This may help:

Attachment 28340