The Stovebolt Site Forums The Shop Area The Electrical Bay Ballast Resistor

I've never seen a ballast resistor on a 6 volt system, so I am assuming you have a 12 volt system.

In a 12 volt system a ballast resistor reduces the amount of voltage (and therefore current) in the primary winding of the coil while the points are closed. This reduces the heat in the coil and the current handled by the points, making them last longer.

It also reduces the amount of voltage available from the coil to fire the spark plugs. That isn't a big problem once the engine is running, the generator (or alternator) is charging and the battery is fully charged. BUT (big but) when the battery voltage is lower while the starter is engaged (especially in the winter cold) the ballast resistor reduces the voltage to a lower value, reducing the spark even more. To get around this problem a "bypass" circuit provides battery voltage directly to the coil primary, which results in a better spark while trying to start the engine.

The common way to bypass the resistor is with a separate "start" position on the ignition switch or the 4th terminal on a starter solenoid if you have one. On older vehicles (you don't give the year of your 3100, Tricordati) with a "stomp starter" you can replace the switch on the starter with one that has an extra terminal on the side and attach that terminal to the coil primary connector.