Cummings engine tach not reading.

[aloysius]

My starboard cummings engine does not want to run very much. It's strange because it will shut off on it's own. The tach seems to jump all over the place (I've even seen it go backwards past zero rpms while the engine is still running. The sync gauge (which has never worked) is doing a dance also.
Another clue is sometimes when I try to start the engine, the low oil pressure alarm does not sound. If the alarm does sound, the engine will start but like I said the tach swings all over even though the engine sounds to be running at a constant RPM. I observed that the hour meter for this engine seems to not be counting the hours correctly either.
Does anyone know how I can get ahold of Carver to see if they have a engine and helm wiring diagram for my 2000 Carver 406?
Any advise would be highly appreciated.