Factory ammeter

Yes. Chrysler seemed consistant with that. Red for battery connection and black for alternator output.
The back of the ammeter may even have R next to the stud for the red wire. At least on mine, there was no mark on the side connecting to the alternator/main splice.

In '67 the wires were 12 ga. '75 might be 10 ga ?? Cars with the rear window defroster grids got 8 ga!
I'd suggest 12 AWG Marine wire at a minimum, and 10 ga would be better. Marine wire is made with smaller strands and is slightly denser for the same gage diameter tha automotive gages. I find its also easier to work with. Due to the restrictions on in-person retail I ended up ordering 10 ga GXLautomotive from Wirebarn for the main run to the stud.

The ammeter studs were #10 and the alternator output stud 1/4" diameter. Look for ring terminals with decent contact surface but not so big as to risk easy shorting.
I saw a lot for sale on-line that had insulation that looked like it would get in the way of the connection. :(
The ring terminals I bought were 'F-crimp' - IIRC made by AMP - TE Connectivity
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They were actually a bit of a pain to work with. I had to trim the wings a little to fit the wire tightly and due to the thickness they didn't crimp easily.
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Then heat shrink tubing to cover the crimp area.
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For something to compare the condition of yours to. This was the condition of the bulkhead terminal from the alternator when I checked on it in. The rubber seal had melted and there is slight discoloration of the metals but overall not terrible. This is part of a 25 yr old replacement harness. I'm pretty sure the damage was done 2016 when I was forced to recharge a very low battery off the alternator.
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