Atleast I think that is what this plastic tube is. My question is what does it plug into??? It was just dangling right under the end of the air intake. I took a couple of pictures for reference. I thought it looked like maybe it plugs into the top of that brake booster or whatever it is with the hardlines running out of it. I pushed on it pretty hard but no luck. Can anyone help me out? Thanks.

 

Follow it up and tell us where the other end goes.......This will help.

 

Turns out this line is to engage the 4x4 hubs. I opened the hood on a brand new F-150 4x4 and this line was just clipped onto one of the ABS hardlines. It didn't go anywhere either. Seems odd to me but oh well...