Of course you will use the correct size terminal for 12 ga wire but even so, those are not as strong.
The factory ring terminals are heavier, have more surface area, and have wire support - also called strain relief, and a rubber seal to the wire insulation.
I found much of the under dash wiring has very little slack. There may not be enough wire length there to install without straining the wire and terminals.
1969 Dart
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