OK I have a pretty good handle on the vacuum system of my 95 4.3 blazer 4x4.... there's one line I'm not posative of and just want to confirm... there's the main feed comin' off my intake... goes to the check valve then off to a T the main line comes across the firewall inside a case with a couple wire bundles and over behind my brake master cyl. now there's another line that comes across the firewall in that bundle of wires one end goes behind the master cyl. on one of the T's in there.. .the other end goes to about mid firewall then runs down under the vehicle and back underneath it and disappears... I haven't crawled under there yet to trace it down but is this the line to the transfer case???

 

Yes, It provides vacuum to the t-case.