With a transfer case you shouldn't have an output on the trans. There should be a round adaptor on the end of the transfer case. If the cable is not connected, you should see a square hole in it for the cable. The cable runs from there to the speedo, or from there to the transducer on the fender for the cruise control, then another cable runs into the cab to the back of the speedo.
Speedo's can also go bad, so if the cable is hooked up, grab a drill and have someone run the drill while you watch the speedo. The speedo could be good and the plastic gear in the TC could be bad. Or the cable could have come out of the back of the speedo.
If the speedo moves with the cable, and was hooked to the TC, lift the rear wheels of the vehicle, put the TC in neutral, and rotate the driveline. You should see that little square gear turn, if it doesn't the gear is bad.
There are lot's of little things to test for the speedo.