I Have A 1996 Ram 3500 And The Speedometer, Air Cond And Alternator All Quit Working At Same Time. Has Anyone Seen This And If Not Does Anyone Have A Schematic For The Pcm

 

I have had exactly your problem, on my 98 12alve, not sure if they work the same. is yours a manual or auto? cuz my tranny didnt work well too, it didnt take al gears.
It was the crank sensor!

I learned it the hard way its NOT the pcm, i bought a new one $550 and my old one as a core, still got no comunication with a scanner!

The wires where burnt at my crank sensor, maybe you need to replace it, or also... it has to be very very close to the wheel to measure the rpms, and to make the PCM work!

(Note: the crank sensor is in the front of the engine, on the lower side on top of the wheel that bolts on with 4 bolts 15 mm)