A good deal of confusion surrounds the subject of ignition coils in cars with positive earth systems. In this chapter I argue, with some diffidence, that the conventional wisdom is wrong, that a number of papers which I believe are poorly researched and misleading have been printed and disseminated, and, worse, believed, and that the errors have been reproduced and reprinted so many times that they have acquired the patina of truth. I am aware of the dangers of contradicting the dominant paradigm, because "Where no counsel is, the people fall; but in the multitude of counsellors there is safety" (Proverbs 11:14 KJV). On the other hand, "The simple believeth every word; but the prudent man looketh well to his going" (Proverbs 14:15 KJV). Moreover, "There is nothing so absurd that it cannot be believed as truth if repeated often enough" (William James 1842-1910), and "The fact that an opinion has been widely held is no evidence whatever that it is not utterly absurd; indeed in view of the silliness of the majority of mankind, a widely spread belief is more likely to be foolish than sensible" (Bertrand Russell, 1872-1970) . These sentiments have been verified experimentally in scholarly works: have a look at Solomon Asch's work on conformity, and Hasher and Goldstein's work on how the repetition of more or less plausible statements affects one's judgement of their truth and validity.
It takes only about 10-14kv to fire the mixture under operating conditions. Once the spark is struck, its polarity doesn't matter, and it makes at least a few cycles of alternately positive and negative excursions before the energy initially stored in the coil's primary is dissipated. (This would explain why the graphite pencil test described in mgaguru's first paper is hard to interpret, since during one excursion electrons will be flowing in one direction, but in the next they will be flowing in the opposite direction: in one excursion the flare will be between the pencil and ground, and in the next, between the pencil and the HT lead. The excursions are so rapid that it looks as though the flare is going both ways.) This oscilloscope trace shows the ringing when the points open, causing the spark; the second, lesser, ringing is when they close again, to allow the current to build up in the primary. In the sketch above this secondary ringing is not shown when the points close. Other images and discussion can be found easily; the image on the right comes from Steve Maas's paper, referenced earlier. And although it's commercially driven, this one is a good resource. See also this thesis which was prepared for a MSc degree.
So, parallel or series connection: which is correct? I have long ago forgotten all my circuit theory, but I thought that the manufacturers of the coils would probably know, and would have a preference. They probably expected the + terminal to be connected to the battery, which as we've seen is almost always positive these days, and the - to ground. That meant that they wanted or expected the parallel circuit as shown in A above. And also, of course, the + corresponded to the old SW, and in the old days of SW and CB, connecting the SW to battery would have resulted in the parallel circuit for both positive and negative earth systems, with a negative-going pulse in the case of negative earth systems, or a positive-going pulse in the case of positive earth systems. So in my case, that meant connecting the + terminal on the coil to the - terminal on the battery, via the ignition switch of course, and the - terminal to ground via the contact breaker. So that's what I did. The car works well, and any remaining problems must be due to some other cause. We will see.
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