I was under my truck the other day (2002 F-150 4x4) and noticed something weird. On the frontside of the transfer case (facing the front of the truck) i see what looks to me like a fitting for a vaccum line with nothing plugged into it. Its a tappered nipple with like 3 or 4 notches on it. Would like some help identifying what it is. Thanks in advance for any help.

 

Most likely a vent that the hose has fallen off. Got a pic?