Have 1999 ford f250 superduty diesel .4wd was fine one day next day no 4wd and no 4wd kites in dash.
Chkd fuses,4wd module,shift mtr will work if has power,no power at shift mtr. Or at switch
on dash.what should I chk next
remove shift relay block under hood, look for corroded wires to UNDERSIDE of relay sockets. common issue, under reported. in mean time, take cover off two relays, use your finger to close relay contacts, shift should work fine. what happens is open condition closes when downward pressure from volt/ohm meter is used to check continuity......then reopens when pressure is removed, drives you batty.
Search Ford F-250 Super Duty Questions
Ford F-250 Super Duty Experts