The 6 volt coil was commonly fitted on British cars in the seventies. The power feed to the coil passed through the ballast resistor cutting the nominal 12v down to around 6v. BUT when you are starting the engine, that is cranking it on the starter motor, the ignition key switch sends the full battery voltage to the coil. The idea is that with the coil overpowered you will get a stronger spark and the engine will start more easily. As soon as you release the key, the ballast resistor is put back in circuit and the coil then operates on 6v.
It is my understanding that most, if not all, electronic contact breakers require you to by-pass the ballast resistor and provide the coil with full battery power at all times.
Hadn't much time to read lately but I see I'm just back in time.
Running 12v through a BALLASTED
type coil will have twice the amps through the electronic ignition module and will destroy it instantly or in case with a Lumenition within 10 minutes. Some quality products like the 123ignition can switch a 1 Ohm minimum coil so you can bypass to have advantage of the bigger spark during normal running. The Lucas BALLASTED coils, 1,5 Ohm, cannot handle the extra current itself and will go faulty but a Bosch BALLASTED coil, 1,2 Ohm, can handle the extra current without it's resistor and can be fitted this way on for example an 123ignition.
The Lumenitions and the cheap 25gpb points replacement kits made in China sold as made in UK cannot go lower than 3 Ohm resistance so these need a conventional 3 Ohm coil or a 1,5 Ohm BALLASTED coil incl. the 1,5 Ohm resistor to have a total of 3+ Ohm again.
The electronic ignition should be fitted on a 12v feed and not on a BALLASTED coil as this feed is reduced by the resistor.
You can check when starting there should be battery voltage during cranking on the white/yellow wire connected to coil positive. The white/pink is the ballasted feed.
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