I do know from experience from my 2001 1500 with the dana 44 you can get a lot of issues with the vaccum lines, ive had the line where it connects into the axle come loose and can make it really hard to put it into 4wd or come out of 4wd depending which side comes loosest, usualy when im towing my trailer on and off the dunes. also if its vaccum part of the line that runs along the frame is metal but runs right by the exhaust manifold and ive had one line melt there before and it made it take driving down the road for miles before it would come out of 4wd. i just bought a 06 2500 cummins with the auto transfer case and havent looked at it enough to see if its got any vaccum lines or not, hope this might help.

 

My 4x4 indicator light was not working on my 2005 Ram 1500. I unplugged the two-wire plug on the top of the transfer case and jumpered the wires. Presto! The 4x4 indicator light came on. I unscrewed the 4x4 switch off of the top of the transfer case and plugged the pigtail wire back into it. I had my girlfriend sit in the driver seat and watch for the 4x4 indicator light to come on as I pressed on the plunger-style switch. Nothing. The light wouldn't come on. Bad switch. I called the dealership. The part is called the "4 wheel drive switch" and costs about $35. Very easy to change out.