ignitor or coil - The tach gets its signal from the coil/dizzy assembly. if the coil or ignitor is bad, the gauge will read zero.
Can't tell you which one, but one of those. There was a recall on ignitors on our cars..it is a small 'D' shaped thing with some connectors on the ends...inside the dizzy. If I remember another discussion correctly, the BAD ones originally are black, and the new ones that Honda put in were brown (if it was replaced before you owned the car.) You should be able to call up Honda and get it replaced for free after they check your VIN. They'll have a record if it is was done. Or you can get one from Auto Zone or equivelant for about $65, but I never trust ignition/electrical parts that aren't OEM.
The days of that continuing to work are numbered, don't trust your car to get you anywhere 'til it's fixed.
