I would bet you still have problems in the major power distro. IT IS RARE but tuck this away: A few inches from the ammeter, in the black ammeter wire, is a factory WELDED splice, which can break. That feeds the ignition switch input, the headlights only power to the light switch, the fuse panel hot buss, and varies, but sometimes other components in some years.
The bulkhead connector would be high on my list, and the ammeter connections, terminals, and ammeter itself
This is a simplified diagram from the MAD electrical page of the primary power
Every major point in this diagram is a potential failure point. The power comes off a tag off the battery, and runs to the starter relay "big stud." This is not only one of the relay contacts, it acts as a junction.
From that stud, a wire with the fuse link runs to the bulkhead. Could be the eyelet to the wire at the relay stud, in the link itself, or in the bulkhead feedthrough terminal. You can see there are three major feeds off that splice, then the black continues on through the bulkhead connector and out to the alternator.
You simply have to follow through all of that and see where you are losing it.
One last time, I would concentrate FIRST on the bulkhead connector. BIG issue and BIG on probability
From the buikhead the power goes to the ammeter. Here you can have a poor connection in the factory crimp from the wire to the eyelet, problems inside the ammeter itself, or the eyelet terminal on the black wire coming out.
Then on to the welded splice, which again can fail
