You can do what I did on my 1986. I bought this switch.
DPDT-CO 30 Amp Momentary Toggle Switch GlideForce SWT-TOG-MOM-4W, Toggle Switches, DPDT-CO 30 AMP MOMENTARY TOGGLE SWITCH, 30 AMP 12 VDC REVERSINGGlideForce,SWT-TOG-MOM-4W ,
www.surpluscenter.com
I bought a 30 amp circuit breaker and mounted it to the battery + terminal. Ran two wires from the circuit breaker and the - of the battery into the cab to the new switch. Coming off the switch I ran two more wires out of the cab and down to the transfer case. I snipped the two motor wires and wired my two new wires to the motor.
If you look at the switch, you will see a "X" on the back of the switch. This switch is setup to forward and reverse a dc motor, which the transfer case motor is. So when you move the switch, the transfer case motor will go one direction or the other, engaging the different transfer case modes.
Some comments about the above modification; It works very good compared to the computer system that may or may not work when you need it. You can count on this simple system to always work if your motor is good. But;
They must have supplied the motor originally with something less than 12v. With this modification the motor seems to move very quickly. So it is best to "bump" the switch when moving the motor.
You are in the dark sort of, moving the motor and feeling what gear the transfer case is in. Sometimes you might get it on the edge and it will grind until you bump it a little more or bump it back to fully engage the proper mode.
A important note; YOU MUST BE STOPPED TO USE THIS MODIFICATION. If you have your wits about you, and your hubs are already locked in, you could shift it on the fly, but there is a danger of moving too far and engaging 4 low. So I would err on the side of caution and stop while using the switch. Also, I never had little kids in the my truck by themselves. I can see you driving down the road and a child playing with the switch or accidentally knocking it while driving, which would not be a good thing. If you were afraid of this situation you might could use another lockout switch somewhere so the direction switch would not work.