A performance canister coil wired straight to a stock points ignition will draw more current than the points are meant to switch, which burns them quickly. This 0.8 ohm ballast resistor sits in the coil feed to limit that current. It is not needed if a 6 or 7 Series ignition control is doing the switching, because those units limit current themselves.

MSD 8214 Coil Ballast Resistor Features:

• 0.8 ohm resistance value.
• For use with a performance canister coil on a stock points ignition system.
• Not necessary when a 6 or 7 Series ignition control is used with a points distributor.
• Intended for older points style ignition systems.