I have a 5.4L 1998 F150 and the 4x4 engaging vacuum motor that won't work. I traced the problem to a disconnected 3/8" rubber hose under the battery box. One end is connected to the vacuum motor on the front axle, but the other end is not connected. I took off the plastic covers on the electric cables, and the cover over the air intake, but I can't find a vacuum source to connect this hose. Anyone have an answer? What am I missing?

Thanks!

 

Grant, below is a diagram. Hopefully this will help.