I just had ball joints installed on my truck. My friends shop mechanic found that I had a torn driveshaft boot, So I decided to put one on while he had it open. He called me back and said he found a vacuum line on the drivers side down by the driveshaft that went no where. He checked all over and there is no spot for it to be attached. He couldn't quite get in to see if there was one on the drivers side. He checked the whole 4wd system out and ran it through the paces; Everything works fine. Is this some kind of vent, Or should it be hooked to something? He said its not pulling vacuum at all.

 

Two lines (they are joined if they are the facory originals) come off the IWEs. The larger is the actual vacuum, and the smaller is a vent line for the IWE. Both sides are the same in that manner. For future reference:

https://www.ford-trucks.com/forums/836438-everything-you-wanted-to-know-about-the-iwe-system-and-then-some.html

The 4x4 system is both easy to trouble-shoot and repair. Your friends' mechanic should already know about this, as he's working on Ford trucks.