Adding on 2 circuits

65 Dartman said
just out of curiosity what size wire would you call a BIG *** wire? 10 or even 8 gauge? 65’s used, I believe, 12 gauge. According to the 82 J Bodies FSM, they still used 12 gauge from the alternator - my engine compartment wiring is loosely based on a combination of J and early A wiring

It depends on the length of the wire/cable and what the amp load is going to be. There are a multitude of charts available to help you determine the correct size you need. Just Google it. No guess work is needed. It's all been carefully researched.