Originally Posted by Dick Geving
If the inverter/ battery charger is involved, the tach quits.
I would believe the other Dick posting may be close to the issue. In our case, with the engine running and the tachometer not registering, then with the inverter on line and a demand such as the toaster, the tachometer rose to the correct RPM. Turn off the toaster and the tachometer dropped once again to zero.
The next morning underway with the thinking the tachometer was out for the trip home, I was presently surprised to see the tachometer registering the correct RPM and it has to this point and will I am sure. In our case, I believe knowing the alternator tachometer post is internal I will use the word "Pre-charged" ,activated itself under a steady consistent load. Other than that Dick it remains 'Magic, pure magic' and I will not challenge magic!!