I have a 98 F150 4x4. The 4 wheel drive did not work, although the indicator lights came on and the transmision sounded like it locks in. I switched the two vacuum lines on the cylinoid on the front axil and now both 4 wheel hi&low work.
The only problem is that the front end stays locked in all the time. Is there a vacuum leak somewhere or is there a control box somewhere that is bad?

 

Anyone? I still cannot figure out......