You got me curious so I began looking in my service and parts list manuals. It looks to me that the tachometer is mechanical. So you have three places to look bad meter - bad mechanical cable or pick off at the engine.
I would go behind the panel and unscrew the cable at the meter. Then start the engine and check if the cable inner core is turning. If not then the problem is probably with the cable. On my car speedometers, which use a similar system, I've had cable breaks several times. You might try putting some lubricant down the cable if you think that might help.
It's possible that an auto speedometer cable migh work and that would probably be cheaper that JD.
