weird alternator symptoms

[alexlula]

Hey guys, i have a 92 na miata and my charging system is acting weirdly, my faulty alternator light is on but the higher the rpm the more it dimes out wich would indicate a weak alternator but my voltmeter is showing otherwise, at idle its at between 12.3 and 13.8 amd at 4k its at 16.3 what could be the problem?

[— kung fu jesus —]

What is the reading at the battery while running?