I believe that the wandering readings are due to the voltage fluctuating on the low end. When my regulator went and the voltage did its steady drop, at a certain point it would lose its mind and the readings were all over the place.
When the voltage drops below 11.0 volts it will shut the engine down as a safety feature. Its probably more that the computer running the EFI goes down then the engine is starved for fuel and quits.
Ever since I replaced the regulator with the H-D unit, everything is stable and charged.
