Dont have diagram. First place id check is the motor that kicks it in 4x4. There really bad to go bad. The 2nd place id check is the flip swith on the dash. If my memory recalls you have the twist button.
put a new fuse in turn the key to start the truck and it blows the fuse even when its not in 4 wheel drive but when i turn the **** on the dash the 4 wheel dirve light still comes on and the transfer case is still engaging just not the hubs changed the modular thing on the passenger side front corner that has the hubs vacuum lines hooked to it but i tested it and it dont seam to be getting any power to it