Coil Polarity Explained

For those who may be "electrically challenged" I found a couple articles that go into more depth and explain why battery powered ignition coil polarity DOES MAKE A DIFFERENCE and might explain why the coil designer and manufacturer places those + and - labels on coil terminals. The topic concerned battery powered coil distributor ignition as I understood it and NOT Magnetos which, unfortunately, if they produce a spark each 180 or magnetic rotor rotation, operate on different polarities since the North and then South magnets pass by the coil and induce voltage therein. THAT BELOW CONCERNS WIRING AND POLARITY OF BATTERY POWERED STAND ALONE COILS, NOT MAGNETOS.

As the old saying goes "People are entitled to their own opinions, but NOT their own facts" lol and as far as I'm concerned, a person can wire his ignition coil any way he pleases, its his tractor and his choice, you get no argument from me, take it up with the authors of the articles, I'm only the messenger. That being said and based on my own experience and knowledge (past used tractor dealer and retired electrical engineer) I choose to wire my ignition coils at their correct labeled polarity BUT OTHERS MAY CHOOSE TO WIRE THEM AT OPPOSITE POLARITY AND THATS FINE WITH ME, TAKE UP YOUR ARGUMENTS WITH THE AUTHORS OF THE ARTICLES IF YOU THINK THEY ARE WRONG. I'm not here to defend them or disagree with them, I make my own choices as I understand the electrical considerations, even if it happens to agree (as here) or disagree with the articles. I've never seen an article that suggests you should wire a coil OPPOSITE from its labeled polarity?????

Best wishes yall, hope these articles help explain to non electrical gents why ignition coil polarity DOES MAKE A DIFFERENCE, but again, do as you please, that's what I do and yall should do the same.


Coil Polarity 1: http://www.chicagolandmgclub.com/techtips/general/574.html

Coil Polarity 2: http://mgaguru.com/mgtech/ignition/ig104.htm

John T Too long retired Electrical Engineer and rusty, so no warranty on the articles or my dusty brain cells lol wire your coils as labeled or not.

Hey thank you for this very important imformation. When I use to help out my uncle in his shop I would find cars wired up wrong. the Scoup would show the pattern upside down which met some body thought they knew how to do. I mess those days when cars had this type of system now there computers. Just think at one time we said some day we will ask a car what is wrong and the answer will come up. L.O.L. bring your old car in for a tune up at the delarship (not one person will know how to do it). This type of stuff is no longer taught to the meachanic ( it is old school). Brent

Pretty good articles. Like you I prefer to wire them up correctly. I do think there's enough overage built into to system to negate the drop until components start to deteriorate. That's when insult adds to injury. As the old saying go's I would like to have a quarter for each one I've swapped back over the years.lol

M Man, I don't know if you were acquainted with my departed friend Duane Larson, a Nuclear Physicist, but he and I discussed this topic a lot, so he ran his own experiment. He found if the coil was wired at the incorrect opposite polarity, the voltage necessary to fire the plug was like 3 to 4 thousand volts HIGHER. Indeed, correct coil polarity DOES MAKE A DIFFERENCE as I, an electrical engineer, am aware, but I can understand how some non electrical trained people may be of the opinion it makes no difference if wired as the designer and manufacturer labeled it (+ and -) or wired at opposite polarity. Can anyone find an article that says WIRE COILS AT OPPOSITE POLARITY AS LABELED FOR IMPROVED PERFORMANCE!!!!!!!!!!!!!!

John T

You're welcome Brent. Yes the old days are overrrrrrrrrrrrrrrr lol. As I asked above, can anyone find an articles that says you should wire coils at their opposite labeled polarity to improve performance???????????? The designer and manufacturer had a method and reason for those + and - labels on coil terminals, if it made no difference as some think, I doubt they would have labeled them as such. Again people should wire them as they please NOT what those article or I may happen to think.

John T

Thanks! This makes a lot more sense now.

Found this in the second article, which confirms my theory that the COIL doesn't care about polarity:

"A transformer is not affected by polarity, since it is an alternating current device, so it matters not to the transformer what the input or output polarity may be. Any polarity on the primary side and any polarity on high tension side will produce the same quality of spark."

And then this concerning the SPARK PLUGS that do care about polarity. Would have never imagined this!

"As electrons go, they love to jump away from a hot surface and fly toward a colder surface, so it is easier to drive them from hot to cold rather than from cold to hot. 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. Oddly enough, this has nothing to do with polarity of the vehicle electrical system, but it is influenced by the common connection inside the ignition coil."

Who figures this stuff out! LOL

Brent, did you know ignition 'scopes typically invert the ignition pattern, so the negative-going spark pulse is shown going upwards (+)?

I would GUESS they do that to make reading the spark voltage on the graticle more intuitive, higher is more voltage.

So when we are viewing a nice ignition pattern on an ignition scope we are actually looking at it upsidedown!

You're welcome Steve, yep I had read similar type of coil polarity information yearsssssssss ago, and even before (based on my own education and experience) I chose to wire coils at their labeled polarity NOT backwards. True, they still "work" if wired wrong and if people insist on doing so for whatever I cant imagine reasons.

Take care, I enjoy your posts

John T

Yo Steve, PS as far as the spark plugs, if the coil is wired correct as designed and labeled, THEN THE SPARK ACROSS THE PLUGS GAP IS CORRECT AND MOST EFFICIENT (Hotter electrode tip to cooler ground strap). That's why the coil should be wired at its correct designed and labeled + and - polarity so the plug fires at the corresponding correct polarity.

Are we havin fun yet???

John T

Just my 2 cents worth on the topic as in the past I have come across coils that were not marked for + and -
Old school way of checking polarity as I recall was to remove a plug wire and hold it a 1/4" from the block, run the engine and hold the pointed end of a pencil between the wire end and the engine.
You then can clearly see the direction the spark is jumping.
If it jumps from the pencil to the block all is well.
If it jumps from the block to the pencil then you are hooked up backwards.

John, thanks for the links.

I've been a long time believer that the coil doesn't care about polarity but the spark plugs do, as upheld in these articles.

I'm convinced from real life hands on experience. I've encountered at least a half dozen old tractors that were stubborn to start on first attempt in the morning, even on a warm summer morning. Checking, I found the coils wired opposite from battery polarity. Reversing the coil connections to match battery polarity made obvious improvement in starting.

All of them were 12 volt, originally positive ground, but converted to negative ground. I presume that the coil connections were overlooked in the positive to negative ground conversion.

Yep, and if the coil is wired correct as designed and labeled (NOT backwards) that causes the plugs to fire at the correct corresponding polarity which is why how you wire the coil DOES INDEED MAKE A DIFFERENCE.

Fun chat, take care and happy Fourth of July

John T

We are fortunate that electrons love to jump from hot negative electrodes to cooler positive places. It allowed us to have vacuum tubes and Marshall amplifiers and Jimi Hendrix.

Zeke B.

YES vacuum tubes had a glowing "heater" under the Cathode to heat it up so electrons flowed easier to the cooler Plate/Anode

Plenty of those tubes in my Zenith and Crosley and Grunow and Hallicrafters and Hammarlund antique radios

John T

(quoted from post at 11:05:32 07/03/15) Yep, and if the coil is wired correct as designed and labeled (NOT backwards) that causes the plugs to fire at the correct corresponding polarity which is why how you wire the coil DOES INDEED MAKE A DIFFERENCE.

Fun chat, take care and happy Fourth of July

John T

Click to expand...

o reason not to do it as "right" as you know how.
My complaint is the logic people use to "explain why", such as cold starting improvement testimonials or the "40-50%" loss when done backwards! Clearly at cold start both spark plug electrodes are at same temperature, so thermionic emission is irrelevant.
40-50% or 10,000 volts "loss" or whatever number Bill Joe Bob Bubba wants to pull from the dark hole, are meaningless numbers that anyone can post in any article on the internet, mag, wherever, MG club or tractor club or MC club. Look at the voltage on a scope and it is so small as to be a subjective judgment. Wire it "right", just don't use wrong justifications.

Many years ago when I taught ag for short time took class to a cousin shop to pick up an IH H.We were going to take the tractor back to school for tune up and general check over, fluids etc. Cousin and I were chatting a bit when he said you fellows will have to pull start the H as it will not start cold.About the end of our short conversation my shop boys started the H and drove it up to his house. He said how did you fellows start the thing, it always has to be pulled when cold. My boys answered you had the coil hooked backward. We switched the polarity then it fired up.

Yep, it DOES make a difference - I can't really explain why but I think [b:e33ab4f957]John T[/b:e33ab4f957] did

It has been noted ; it matters which way your battery is grounded [ or should I say landed to the frame]. The kill switch ,if added ,will always go on the points side of the coil.

This has a picture of what I was taught in Auto school. Jim
Picture of test link, scroll down

You say "Wire it "right", AMEN TO THAT BROTHER I certainly agree, that's how I did it long before YT Mag was around lol

John T

All this electrical talk is over my head. Please just tell me if the tractor is positive ground, which post on the coil goes to the distributor? Confused Chris

John T, I remember Duane well from years ago. I was aware of the tests but coulden't remember the difference. Do you remember the majic number of volts necessary to fire the plug or do gap differences make this impossible? I ask because I'm curious as to how much overage was built into a distributer system. I'm sure the reversing polarity of a magneto was the reason behind it but I'd like to know how much.

how do you get the magnets correct when they are glued into the flywheel?

If the battery is positive ground, the positive terminal of the coil connects to the distributor, assuming the coil is marked "+" and "-".

Zeke B.

In a battery /coil ingnition there are no magnets involved.