So have a lot of other stuff going on, but did get a chance to get a grounding strap from motor to body installed in factory location. Double checked with meter and got good ground. Also double checked VR ground and it is good as well. I also removed leads from ammeter, cleaned them up and then installed an aftermarket ammeter using those leads ( was thinking maybe it was the gauge itself).

Good news is that seemed to solve the problem, got 14.4V at battery idling, and all other voltages were consistent, and gauge didn't peg to charge when revved.

But I couldn't leave well enough alone. I'd prefer to use the car's ammeter , so I re connected cleaned leads to gauge, restarted car and voltage dropped to similar reading of 12.5V at battery idling.
So I thought 'ok it was the gauge' . So I reconnected aftermarket gauge with those leads, and my voltage stayed the same at 12.5V and change at idle.

Rechecked connections, even took off bulkhead connectors (again), cleaned and reassembled again, no change.
So back to square one.

So, when you moved the wiring under the dash to reconnect the factory Amp gauge, and things changed, it would lead me to believe you either shifted a poor or loose connection that may have been ok before you moved it. It may be time to start giggling each wire under the dash. I would start at the dash and move towards the bulk head connector, one wire at a time, starting with the wires in the amp gauge circuit, or wires from the ignition switch that may have been moved. Its going to be a pita to find which wire connection is at fault. It won't be fun, but I'm betting that is where your problem is.

I had a 69 Chrysler that had a loose connector at the bulk head. I cleaned them all, and they all felt good pushing them back together, but that terminal that was causing the intermittent problem grew worse rather quickly. That one connection at the bulk head was clean, but just a little loose. Hit a bump on the road wrong, and the connection went from good to barely good enough, and finally to not at all. But as soon as the wire was wiggled, all was good again. t took me more then a month to find that one!

So, when you moved the wiring under the dash to reconnect the factory Amp gauge, and things changed, it would lead me to believe you either shifted a poor or loose connection that may have been ok before you moved it. It may be time to start giggling each wire under the dash. I would start at the dash and move towards the bulk head connector, one wire at a time, starting with the wires in the amp gauge circuit, or wires from the ignition switch that may have been moved. Its going to be a pita to find which wire connection is at fault. It won't be fun, but I'm betting that is where your problem is.

I had a 69 Chrysler that had a loose connector at the bulk head. I cleaned them all, and they all felt good pushing them back together, but that terminal that was causing the intermittent problem grew worse rather quickly. That one connection at the bulk head was clean, but just a little loose. Hit a bump on the road wrong, and the connection went from good to barely good enough, and finally to not at all. But as soon as the wire was wiggled, all was good again. t took me more then a month to find that one!

battery to bulkhead
bulkhead to amp meter
amp meter to ignition switch power
out through run or start.
back through the bulkhead
that line has a splice in it.
power goes to the VR, Ballast and Alt all from the same source.
so for a 2 field alt one field reads battery voltage, the other is coming from the VR.

Sounds like a bad amp meter circuit or gauge to me, try using a volt meter with that circuit bypass with a good jumpers or wire clips jump around it on the bulkhead connector

So have a lot of other stuff going on, but did get a chance to get a grounding strap from motor to body installed in factory location. Double checked with meter and got good ground. Also double checked VR ground and it is good as well. I also removed leads from ammeter, cleaned them up and then installed an aftermarket ammeter using those leads ( was thinking maybe it was the gauge itself).

Good news is that seemed to solve the problem, got 14.4V at battery idling, and all other voltages were consistent, and gauge didn't peg to charge when revved.

But I couldn't leave well enough alone. I'd prefer to use the car's ammeter , so I re connected cleaned leads to gauge, restarted car and voltage dropped to similar reading of 12.5V at battery idling.
So I thought 'ok it was the gauge' . So I reconnected aftermarket gauge with those leads, and my voltage stayed the same at 12.5V and change at idle.

Rechecked connections, even took off bulkhead connectors (again), cleaned and reassembled again, no change.
So back to square one.

Have you checked the female terminal's to assure they have not opened up and are causing a poor connection for current? They sometimes need to be squeezed a bit to make adequate contact with the male terminals . This is especially true after multiple matings ( keep it clean guys )

I had this same problem in my 73 dart, in my case the A/C system had a dead short & was slow draining the battery then when I would start up & take off it would full field/peg it any any speed above idle. still havent dug into the A/C system to resolve it (access in the dash is cranped) but unplugging the 2 wire to the evaporator? took care of it for the time being. RR EDIT pulling a batt cable & voltmeter on amps inline between post & cable confirmed a 24/7 draw

just put the two leads together on one of the posts of the amp meter.
that cuts it out of the circuit completely.
as a temp check.
then I would just splice the two lines together, or replace the meter.
if as you said just swapped it in place of the old one and did not change the wiring.
otherwise you could be dead shorting to ground which would be bad. lol.

I am using the existing wires from the factory ammeter to connect to the aftermarket ammeter. Not sure how else to connect it.

So I can connect both of those ammeter leads together without causing an issue ? I think I read the ammeter is wired in series, so that would make sense.
But not sure how that would help diagnose the situation if power is still going through there. I've taken the original ammeter out of the equation at the moment with the aftermarket one.