my friend has a 2002 f350 with the 7.3l shift on the fly 4x4 i went to put it in four wheel drive and it will not switch do not hear any relay fuses are good. no power down at the transfer case. all i know is that the switch has two ground wires out of the four. What wrong driving me nuts.

 

Mine did the same thing and it was a loose plug at the switch on the dash.