The voltage is OK. If you checked the ignition coil primary voltage with the ignition switch in START, it would be 12 volts. Any electric circuit can get too hot if the resistance ohms is too low. So, if the spark plugs, and wires, are supposed to have a certain amount of resistance; but, the resistance is much lower, excessive current will flow through the ignition coil, and it will heat excessively. Check the ohms of the ignition coil, spark plugs, and spark plug wires.
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In order to test the spark, pull the spark plug from the engine, and then start the car. There should be a bright blue spark between the electrodes every time the cylinder fires, provided that there is enough voltage reaching the spark plug. The coil is likely to be faulty if there is no spark. A digital multimeter is required for testing the resistance levels of the ignition coil.
High Voltage Ignition Coil Supply
Coil Polarity I was converting my older British car over from positive to negative ground when I came across the question of coil polarity. I discovered coil polarity is very much misunderstood. In researching it, I was very confused until I found out there are two definitions of coil polarity. I talked to three or four knowledgeable people on the subject and read several technical books and articles. Everything made sense in itself but didn't jive together until I found out they were talking apples and oranges.
Ignition coils supply the distributor with high voltage electricity to fire the spark plugs. The coil consists of a primary winding coil of copper wire and a secondary winding inside of the housing and in very close proximity to each other. The primary winding is energized with battery voltage by the ignition module or, in older engines, the points. Coils may be of the rising-field type or the collapsing-field type, meaning that the secondary winding which steps up the voltage is excited when the electrical field around the primary is expanding or contracting, respectively, in a process known as mutual induction. Testing the coil can be done with a multimeter and basic mechanical skill.