94 has a different switch
first check the switch and make sure it works, otherwise begin to look towards the shift motor on the T/C. Make sure you have power at the motor (check the plug with a test probe or multimeter) and if you have power but no 4x4 still, give the motor a few taps with something sturdy.
If still no 4x4, take the motor out and turn it by hand, then engage 4x4 in the truck with the motor out and see if it turns.
If still no 4x4, get a new shift motor.