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Old 03-16-2017, 10:30 PM   #323
Karl Buchka
Never go full retard.
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Join Date: Mar 2007
Location: Los Angeles

The polarity of the current never changes for a given pair of spark plugs. One of the plugs in the pair will always have current flowing in the opposite direction of the other.

Here's a random diagram I found on google that illustrates the point:

The circuit for the secondary winding is being completed through the block and the current always flows in the same direction, which means one plug sees opposite current polarity of the other plug.

I have admittedly never given this much thought. If it means the plugs only last X miles instead of Y miles (where X is some 5 digit number) then I'm personally not bothered by it. It's a fair point though, and people should decide for themselves if it's worth getting special spark plugs.
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