Overcharging

Im gonna check the bulk head connections today. They have never been removed. Maybe if I go through the series of events something will jump out at you guys.
I accidently left the key on about a month ago. Didnt kill the battery. Drove it after that. Then a few day later and battery was dead. It was very old. I charged it and got it running. Thats when I noticed the overcharging started. So, new battery, vr, alternator tested and new cm. 15.8, 15.9 volts. Spikes at start up. Wiring has never been touched. Bone stock. I have checked connections br, vr, cm, alt. Any help will be greatly appreciated.
Take photos.
Follow the battery feed as best you can back to the bulkhead.
It may also lead to a grommet in the firewall.
Without a FSM we'll have to figure out the circuit based on what we see. It may be like a '74, but could be different. '76 is very different.