Right. So lets go back to this.
The ammeter was showing battery charging.
Made sense because the battery was low. That was normal.
But..
When the headlights were turned on, it showed more charging!
Clearly that's not true.
The headlights somehow were wired to the battery, or the wire between the battery and the ammeter.
My first guess was a relay system was attached at the starter relay. But the photos didn't show that.
Then he turned on the heater, and accidently the windshield wipers, and the same thing happened.
Therefore the fusebox must also be wired between the battery and the ammeter.