Unable to engage 4wd 1993 pajero

Do the 4 wheeldrive lights in the middle of the instrument cluster flash when you've selected 4 Wheel Drive?. Have you tried move forward with the transferbox lever to 4 Wheel Low on a NON-Asphalt/Tarmac surface[ie, dirt road/trail. Sometimes on a Gen 2 Pajero/Montero that hasn't had the 4 Wheel selection used in awhile, do this trick, before moving the lever back up to 4 Wheel High[with no center diff lock] seems to free up a sticking t-box. Also, make sure all your vacuum hoses for the front axle connection system are attached to their metal pipes or solenoids, esp. the main connection at the engine[your source of vacuum for the system.]