remembering that most 4wd stageas have an open rear diff:
coming out of the main loom under the dash, slightly to the right of the steering column is a small loop (1 wire in it) with a plug in the middle
unplug this plug (has plastic tabs holding it together - can take some fiddling)
start the car, and pump the brake pedal quickly until the 4wd light starts flashing, if you dont pump it enough the 4wd light will come on solid if i recall.
flashing = 2wd
solid = air purge mode
plug it back in when you are done.