Amp gauge shunt

Didn't read the whole thread
The factory Ammeter has a good sized shunt already built into it. I was impressed when I saw it.
The biggest issue is the ancient bulkhead connector; get rid of it. Wire every non-factory accessory, and the headlights, on relays and forget all about your troubles. After I did that in year 2000, I have never had another scary stinky-plastic trip again,worrying if my car is gonna catch fire. I was nearly 70 miles from home the first time I smelled it. I pulled over right there, waited for the engine to cool, and punched thru the melted plastic with a temporary repair,which I made permanent after the trip.
I carry an emergency repair tool kit. You pretty much have to with a 50 year old car, cuz you just never know......
On another car I had to make a fusible link bypass on the side of the hiway, this time on a cold winter day, on my way to work. I had to rob other, non-essential, wiring to get moving. Never leave home without a length of wire and a wire cutter; there are legitimate reasons that some of our cars come to us with hacked harnesses.
On another car I had to replace a magnetic pick-up, this time only 25 miles from home; and in summer,yahoo!
Or a factory ECU. Or numerous Ballast resistors over the years, there is no prophesying when one of those will just give up. And tail-lights; you gotta stay on top of those, cuz 3 minutes after you lose one, your muscle car will be pulled over and the cop will give you a twenty-minute safety lecture!