What I hear is they are default 4wd.
I understand in many models it's a vacuum line that keeps a "clutch slave cylinder" type pin depressed
If the vacuum line works, 4wd can be disengaged, but if not because of whatever causation, it will not be able to let go of 4wd and will remain, even if 4wd stick is in 2wd.

 

Check yours for the cannister somewhere underneath near the transmission, or vacuum lines around a double solenoid (each an electrical plug about thumb size)
Not sure what you've got, but early years are likely to have canister (assumption) rather than the electrical + vacuum solenoids.
Look for a rubber boot , (and not the regular drive clutch slave cylinder boot for standard transmissions), find the boot that entangles with vacuum lines and that's definitely it.
best luck.

 

Theres the second res.


85 montero

85 montero Before

85 montero Undercarriage before

85 montero Engine bay

85 montero Drivers side where hose was disconnected


Nest of hoses