Found my dads original 1971 duster!
Your missing my point.
The board is what it is. It just made me wonder what has been changed.
The ammeter may not be an ammeter - that's what I was getting at.
It should look like the one I posted.
Another view
If the fuel gage is suspect, then take it out and look at it. It can be checked out - there's a number of threads where we've done this - and also factory tech tips.
Follow your nose and eyes. You see a place where the ammeter stud contacted something - well thats the battery connecting and shorting.
The electrical diagram is just like a road map. We don't take every road, we just follow the ones we're interested in. The electrons follow a path connecting them from positive to the negative.