The "left small wire" is the circuit that bypasses the "ballast resistor" between 12v "ign" and coil + when the starter is engaged. Unless you are using points-type ignition, you don't need either the ballast resistor or the bypass circuit.
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My Pontiac is a '57 GMC with its original 347" Pontiac V8 and dual-range Hydra-Matic.
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