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Al..... Jim's got the right answer for why spark coil polarity is important, Edison effect (thermonic emission). Electrons like to go from negative to positive. Claus is correct that the ignition coil is what in other electronic fields is called an autotransformer. This means that there is an internal junction common to both the primary and the secondary winding of the transformer. As I remember it, the common autotransformer terminal is the terminal that goes to the points. The coil polarity has nothing to do with the battery voltage. It has everything to do with the direction of coil windings (CW or CCW) with respect to each other. You are correct that the 1 to 3 ohms resistance of the primary with respect to the 5,000 to 10,000 ohms of the secondary will and should have neglegable effect on the secondary voltage to the sparkies. But its the magnetic field polarity as set up by the direct current in the primary that has a major effect on the enduced secondary voltage when your points open. which is what you have observed by your scope. Your can loose up to 25% of your sparkies with incorrect polarity. All is just fine, as long as the coil produces more than enuff sparkies. Once the ionized gap voltage has been exceeded, pow! ignition. It doesn't matter how much extra sparkies, just as long as you have enuff. Remember the ionizing voltage depends not only on the gap of the sparkplug, but also on the compression, and also on the metalic ion wear that rounds edges of the electrodes (voltage likes to jump from sharp edges) and surface film resistance. Modern sparkplugs really are miracles. I've put as much as 50,000 miles on 'em before I changed 'em in my non-stock '69 BMW 2002. I changed 'em because I was going to the BMW's club driving school at Seattle International Raceway. I really couldn't tell any difference, but boy did I have fun. (grin) It certainly has been a sparkling topic..... Dell
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