After work today, I removed the magnetic pick-up (mounted behind the oil filter housing), cleaned the magnetic probe, and re-installed. What I noticed upon startup was this:
When turning the key to "on", the tach needle barely moves.
The tach still does not function with the engine running.
When turning the engine off, the tach "jumps" to 500 RPM then to 0 when engine is off.

I also checked continuity between the two terminals (brown wire and white wire), coming off the pick-up. Nothing. This might be the problem, as the seal where the wires enter the sensor housing is cracked, probably moisture and crud have done their damage. I used a little compressed air to clean out any crap, still nothing.
I finally found the schematic for the cluster, the tach pick-up is nothing more than a coil with a wire at each end. I think there should be continuity at all times. Even with the engine running, I did not pick up any continuity. (Using a digital meter with audio function for continuity). I am leaning towards replacing the tach pick-up (aka engine speed sensor). Any thoughts? Alan