Dodge Ram Pickup 3500 Forum : “1994 4wd will not lock in.”

check the vacume switch on the t/case and also check the actuator on the frt diff, check all vacume hoses and lines from the
t/case to the actuator and the intake maniold to the t/case, i have seen several times the steel lines and plastic lines will break or rust..

IF ITS THE ACTUATOR...donot just replace it and try the 4wd, inspect the collar and shaft inside the hole...most times its the shaft and collar inside the front axle that wear out and they "slip" apart then bend the actuator (what would happen to the new one)...i learned from experience

99% chance that it is the actuator in the front axle, which has a plastic fork in it.  When you pull out the actuator check the slide lock inside the axle housing along with all your vacuum lines as well.  you should be able to get a brand new one for under 350 from the dealer.  auto supply stores do not carry the item, previous experience