‘83 Voltmeter Questions

[Bob Q]

Just finished up doing the LMC tach conversion in my ‘83 K2500 6.2L. Took it for a ride this evening to double check everything before putting the instrument bezel back on. Tonight, the factory voltmeter starting reading high (15-16 volt range) just before the red zone on the upper end. It’s never read that high and I’ve never had any issues with it up until tonight. I checked the batteries with a multimeter and they were about 12.7 volts with the engine off and about 14.5 volts with it running and the gauge was still reading high. Do you think the voltmeter is going wacky or is there something else that could make it read higher all of a sudden even though the charging system itself seems fine?

Thanks.