76 cherokee 4wd

I have a 1976 cheokee. It has a 360 ford v8, borgwarner transfer case with quadra trac. This is all original equipment to the best of my knowlege. My 4wd is not engauging. Is this system supposed to be full time 4wd? It has a vacuum control switch in the dash with two positions. It has three lines going to the switch: one engine vacuum and two going down to a valve on the transfercase. The lines at the transfercase are getting vacuum. Does anyone know about this system?
I know a lot about cars but this thing is older than I, and I do not have a manual for this dinosaur. And do not have a lot of 4wd expereince.

Any help is appreciated thanks!!!!