Ignition Coil Polarity

[Bob Bidonde]

There has been a lot of posts about ignition coil hookup with regard to polarity. So simply, this post will give you what a correct ignition coil hookup should provide the engine.

Regardless of how you ground the electrical system in your Model "A", the coil's hi-voltage output should travel from the coil to ground via the spark plug bases. That is, the ignition spark should jump from the center electrode of each spark plug, to ground via the gap to the side electrode of each plug. If the hi-voltage is traveling from ground to the coil, the polarity of the coil's low voltage hookup is backwards.

 

[40 Deluxe]

There has been a lot of posts about ignition coil hookup with regard to polarity. So simply, this post will give you what a correct ignition coil hookup should provide the engine.

Regardless of how you ground the electrical system in your Model "A", the coil's hi-voltage output should travel from the coil to ground via the spark plug bases. That is, the ignition spark should jump from the center electrode of each spark plug, to ground via the gap to the side electrode of each plug. If the hi-voltage is traveling from ground to the coil, the polarity of the coil's low voltage hookup is backwards.

Many newer cars use one coil to fire two plugs (thus three coils on a V6, etc).The spark travels from one end of the coil to the center electrode of a plug, across the gap, through the head to the companion plug, then jumps from the ground electrode to the center electrode and back to the coil to complete the circuit. Thus every cylinder gets a spark on both the power stroke and the exhaust stroke. The spark on the exhaust stroke of course, doesn't do anything so this is called the "waste spark" system. So if one plug wire failed, two cylinders went dead!

To save a little money, these cars came from the factory with plugs that had single platinum tips, 3 plugs had platinum only on the center electrodes, and the other 3 had platinum only on the ground tips. So plugs had to go into the right cylinders! Replacement plugs are double platinum.

Thus, half the plugs in these systems are firing with the "wrong polarity"!

 

[Y-Blockhead]

Motorcycles have been using wasted spark ignition for decades. One coil with two secondary leads spark two plugs at the same time.

Batt in______________ to points

 

[Pete]

Another way to explain it:
The primary coil wire end that starts next to the iron core should be the negative or battery negative for best efficiency.