If it would be beneficial, most car manufacturers wouldn't put a resistor in series with the coil, they'd put a step-up converter between the coil instead...
CD boxes do not gain anything, as they have a equal device built in... (they can run as low as 9 volts, to up to 24 volts, with equal performance... Says enough...)

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\'79 lincoln Towncar
\'79 Lincoln Towncar
\'79 Lincoln Continental