Just installed a OEM alternator and new battery never seen this before
I replaced the battery terminals checked all the grounds there are no fuses blown I have put 2 alternators in this car and never had this problem I don’t have any aftermarket radio or amp or anything else hooked up other than factory

 

Sounds like a warranty part swap. It is not regulating the voltage and that part is internal/mounted to the alt. You unfortunately will need to replace it.