Why Pos Ground

Convention has it that the leading edge of the spark pulse to the plugs shall be negative, and this can be achieved by proper connection of the coil, irregardless as to whether the battery is connected for (+) ground, or (-) ground.

BOTTOM LINE if its a 6 volt coil or a 12 thats not internally ballasted, YESSSSS S when I change battery polarity I reverse the coil leads.

Good Luck n God Bless Yall

John T

Positive ground caused less galvanic corrosion where metallic frame members were joined.

Points lasted longer and less pitting at Positive ground.

Its easier to emit electrons from a hotter (plugs electrode) to a relatively cooler (plugs ground strap) surface, Similar to in a vacuum tube where a heater warms up the cathode which emits electrons to the cooler plate.

And finally another Gentleman posted he heard there was less Radio Frequency Interference (RFI) if the frame was at Positive ground.

No warranty on none of this I never actually researched it just recall articles etc over the years which I, unfortunately, didnt save.

John T Nordhoff in Indiana, retired electrical engineer who usually lurks on the Deere pages versus over here on the dark side lol

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Anyway you summarize the majority of the arguments alleging the superiority of positive over negative ground.

One more I’ve heard on occasion: Here in the snowy northeast (where it’s winter except July & August…) positive grounded vehicles experience road salt-induced body corrosion at slower rate than do negative grounded.

However despite all the reasons given, there is no compelling physical theory (or practical evidence) making one ground polarity superior to the other. Both work equally well!

...Bob M (still employed mechanical engineer with a minor in electrical engineering.)

John T

I certainly agree the tractor DC starters turn the same direction regardless of polarity cuz youre not reversing the relative N/S polarities of the Field versus the Armature. However in those light cheap low torque permanent magnet motors (dont use a current induced electromagnetic Field) if polarity were reversed they indeded would run bass ackwards.

I love this sparky chat

John T

The reason is to reverse the motor you have to change the N/S polarity orientation BETWEEN the Armature and Field (reverse current flow direction in either) which a simple polarity swap in an electromagnetic field motor doesnt accomplish. The reason reversing polarity in a permanent magnet motor makes em run backwards is cuz youre changing the magnetic polarity in the armature by reversing current flow direction while the permanent magnetic field stays the same.

Clear as mud ???

John T retired electrical engineer

Your observation is correct only part of the time!

DC motors, with WOUND FIELDS, such as conventional starter motors, DO NOT reverse when the battery polarity is reversed.

That is why you can change a tractor or old car from (+) ground, over to (-) ground, the starter will operate correctly. Also, older motors, such as older heater and fan motors will not reverse with a polarity reversal.

What you have observed is small-engine starter motors that have a PERMANENT MAGNET FIELD. They will reverse when their power supply polarity is reversed. Also, most NEWER heater fan motors are permanent magnet field units, and will reverse when the power supply polarity is changed.