My speedometer/odometer isn't working at all. They weren't working when I got the truck. However, the cruise control does work. Shouldn't that make me think the VSS is sending a proper signal....and allow me to expect the speedo head itself is bad???

1992 D350 Cummins 5-speed

 

If the cruise works that means that the vss is working. Could maybe be bad wiring from the pcm to the speedo or a bad speedo.