Beagle, I've got a 96 model 3/4 ton, but I think they operate the same. First, did you get a indicator light? I have put mine in(thought I did), got a light but no 4x. Just had to move the truck a little and try it again, went in. Next, there is a vacuum operated collar that slides inside the axle to lock it up. If you don't have vacuum, no 4x. I believe it is operated off the movement of the xfer shift lever. I got a manual, I'll look it up to be sure. I'll get back to you in a while.
The manual didn't go into much more detail than what I had already given. I'm assuming that the electrical switch on the vac. motor housing(on the axle) sends signal to the indicator light on dash. What I don't know for sure is what sends vac. signal to vac. motor. It appears, by reading between the lines and without going out and crawling under my truck, that there is some type of valve(?) on the xfer case that would be connected to the shift linkage most likely.