Stock coil with a Vintage Mallory distributor

[tubman]

Again. with an ignition system, you want about 4 amps through the points and coil. On a 12 volt system with a 3 ohm coil, that means no resistor. With a 1.5 ohm coil (usually for 6 volts) you want a 1.5 ohm resistor (resistance in a circuit is cumulative when wired in series). Bottom line is that you need to know what the resistance of your coil is to decide what resistor is needed (if any)..

Ohms law R=V/I 3=12/4.

This is for conventional points systems; it goes out the window with electronic ignitions.