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MG MGB Technical - 6volt coil /12volt coil

Looking for some advice. I have a 78 mgb roadster with a 6 volt coil and a Ballast Resistor wire. Well the wire, for some reason has burnt out and therefore I need to do some electrical work. My question is, Can I just put a 12 volt coil on the car and dissconect the ballast wire? or should I try to get an external Ballast resistor from a different car? I am not very good at auto electrics, so for any answers, please and try to keep the wording in "Laymans Terms.
Thanks in advance for your responces.

Dave Atkinson
D.P. Atkinson

One of the desirable features of a ballasted system is that a full twelve Volts is applied to the 6 Volt ignition coil directly from the ignition switch via a white wire when the starter motor is in use, thus boosting its output and so counteracting the inevitable reduction in voltage that occurs during starting, even in a car that has both a good battery and clean, sound connections. A ballasted ignition coil is designed to produce its output with an input of only 6 to 9 Volts, thus making for good reliability under poor conditions. In a ballasted ignition coil system, the starter relay bypasses the ballast resistor while the starter motor is operating, applying 12 Volts to the ignition coil, thus compensating for the reduced battery voltage. Because a ballasted ignition coil is designed to provide its full output with a reduced voltage, the application of the full 12 Volts produces an increased output, assisting in the initiation of combustion inside of the combustion chambers of a cold engine. One advantageous factor of the 6 Volt ignition coil is that, having half the number of primary windings as a 12 Volt ignition coil, it has half the inductance of a 12 Volt ignition coil, but the condenser value is the same for both. The lower inductance of the 6 Volt coil means that it recharges more quickly when the contact breaker points close again (inductance in a component has the effect of causing the current to build more slowly than in a pure resistance), so it can be used at higher engine speeds without a loss of High Tension output.

However, if you want to change from the Original Equipment ballasted ignition coil system to an unballasted one, simply run a wire from the fuse box directly to the positive (+) terminal of the ignition coil. Removal of the resistance wire is unnecessary, as it will then be bypassed. The bypass wire running from the terminal of the starter relay to the ignition coil should then be relocated from the terminal of the starter relay to a fuse box terminal. Note that the ignition coil should always be mounted with its lead on the bottom. There is an air bubble inside of the coil, for expansion. If the oil covers the internal coil connections, there is less chance of internal arcing from high resistance, such as bad spark plug wires. This internal oil insulation is a sort of third order insurance policy, after basic design and voltage limiting internal spark gaps.
Stephen Strange

This thread was discussed on 02/07/2012

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