Charging intermittent, sometimes it does sometimes not

Well my intermittent issue turned permanent. The whole drive today 20 plus miles was at 12 or slightly below. I had a new alternator as a backup so I decided to swap it in. No change runs at about 12 to 12.1 volts no matter the rpm. Checked connections at multiple points and didn’t see any frayed, loose broken connections. What should I trouble shoot next?