It unscrews, under the speedo cable output on the left rear of the transfer. It´s not listed in any of my manuals, dealer only, don´t know the price?
If your checking it, the port between the two index pins (12 oclock whatever position the switch is) is constant vacuum (goes through a CHECK valve) before reaching the switch. The 9 0clock (next port to left) is 2 wheel drive. The 6 Oclock (opposite the in port) is a vent. The 3 Oclock (or one port to the right of the in port) is 4X. The 4X, also operates the indicator light switch, on the shift motor. A short piece of tubing and the good old suck test, may help troubleshooting.
The steel threads on the switch may have frozen to the aluminum threads in the transfer. A good tight wrench and taping the end of the wrench with a plastic hammer, may help unfreeze the threads. Something your gonna have to do with feeling, I´d take my time and try not to force it with excessive pressure, short jerks often works better, helps break the bond, hopefully without snapping off the threads.
Spraying a little WD-40 into the ports, on the switch, may help free it up, (the piston in the switch), worth a try.