How To: Spark plug polarity

[Hanno Spoelstra]

Mike,

The article is actually about ignition coil polarity. I found it while searching for solutions to solve the ignition troubles on my F15A. I did change the ignition coil polarity as the Ford has a positive chassis ground, and it was one of the parts in the puzzle improving ignition (along with new wiring, spark plugs, condensor and points).

Hanno

As one end of the primary winding in the ignition coil is connected to one end of the secondary winding, reversing polarity of the coil primary side will reverse the drive direction of the spark current on the output side (even though current in the vehicle low voltage wiring still flows the same way). So reversing vehicle electrical system polarity will reverse direction of spark drive.

*snip*

End result is a difference of 15 to 30 percent in voltage required to make spark "initially" jump the gap on the plug depending on which way it is going. So the spark plug prefers to see a voltage potential that is negative on the center electrode and positive on the end electrode for the very first hop of the spark.