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Old 08-03-2013, 09:47 PM   #1
Jim Huseby
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Default POS or NEG ground

There was a comment that an ignition schematic recently posted didn't show whether it was pos or neg ground. The fact is that the spark intensity and the engine's performance will be exactly the same either way, without switching any wires. The only difference it would make is which way the ammeter would read, which also wouldn't make any difference in how the engine would run. Or, to make the polarity situation simpler to visualize you could take the ammeter out of the schematic and connect its two leads together as one wire. If the charging circuit had been included, then the gen would have to be polarized when switching polarity. (Also, recently, it was posted here that though an A generator can be re-polarized, the field magnets will want to revert back to their previous polarity when left to sit for a short period. 'Seems plausible). After a bunch of you argue with me about this ignition polarity topic, and after I explain my comments, some of you will still argue. Here are three questions to get you ready: If your Model A was running a magneto, would the plugs be firing positive or negative ground? What is the function of the coil's primary winding, and where does the primary winding belong in the circuit? Which side of the condensor stores the electrons? Please answer these questions before commenting.
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Old 08-03-2013, 10:12 PM   #2
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Default Re: POS or NEG ground

Either way, is electricity PULLED or PUSHED? Bob
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Old 08-03-2013, 11:30 PM   #3
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Default Re: POS or NEG ground

The coil asks for polarity to be observed.
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Old 08-03-2013, 11:48 PM   #4
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Default Re: POS or NEG ground

The questions posed are irrelevant to the issue. It makes no difference electrically if a system is positive or negatively grounded. The wiring of the coil relative to the system does make a difference however.
It is elementary physics that electrons move more readily from a hot surface to a cooler one, in a spark ignition system that is from the center electrode to the ground strap. The center electrode is hotter than the ground strap, that is where the heat range is determined. So the coil should be wired so the spark jumps from the center electrode to the ground strap.
If the system and the coil is wired so that the spark jumps from the center electrode, then reversing the system polarity, without changing the coil connections, will result in the spark jumping from the ground strap to the center electrode, requiring more energy to initiate.
If you change a stock Model A to a negative ground, and change nothing else, the spark will jump from the ground strap to the center electrode. However, if you then reverse the coil connections, the spark will then jump from the center electrode. It's more efficient that way. It does not make a noticeable difference ordinarily, but may make a difference in a marginal system or starting, or at high speed.
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Old 08-04-2013, 05:20 AM   #5
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Default Re: POS or NEG ground

we need authorative input from tennesee
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Old 08-04-2013, 05:54 AM   #6
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Default Re: POS or NEG ground

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Quote:
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Either way, is electricity PULLED or PUSHED? Bob
I'd rather pull it. I don't like to be pushy. Besides, trying to push electrons is like trying to push a chain.
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Old 08-04-2013, 08:12 AM   #7
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Default Re: POS or NEG ground

PC/SR has it exactly right.
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Old 08-04-2013, 08:19 AM   #8
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Default Re: POS or NEG ground

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PC/SR has it exactly right.
Right, since the coil and generator have a soft iron core the residual polarity can easily be switched back and forth.

BTW, The residual magnetism in my powerhouse is only enough to generate 1/2 volt if I disconnect the filed wire. But a portion of that 1/2 volt is fed back to the field coils and builds the magnetism until the output reaches a much higher voltage. In fact, uncontrolled, the voltage can reach 40 volts.

Jim, you have one of the nicest speedsters I've seen, and I like the color scheme.
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Old 08-04-2013, 08:25 AM   #9
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Default Re: POS or NEG ground

Let's see how good I remember my electronics engineering theory from a long time ago

On question # 1 you may want to restate this one as a magneto puts out AC not DC. So it is changing polarity based on 2x the frequency of the output. Plugs fire on AC not DC.

On #2 the function of the primary winding is to create a magnetic or flux field as current flows through the windings, when this field collapses it induces high P.I.V. in the secondary field, which in this case is called spark.

On #3 electrons are stored on the negative side, actually there are just more electrons on the negative plate than there are on the positive plate when the capacitor is charged.


Electrons like to be balanced or another way to think about it they like to be equal. So they will always flow from a higher source to a lower source.

Way to much theory here that will not help most work on their A.
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Old 08-04-2013, 09:28 AM   #10
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Default Re: POS or NEG ground

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PC/SR has it exactly right.
Let me pile on too.
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Old 08-04-2013, 10:17 AM   #11
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Default Re: POS or NEG ground

It is correct that the coil will work the same no matter how it is hooked up, but as mentioned the spark plug does care. 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 due the reason given above having to do with hot and cold surfaces.
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Old 08-04-2013, 10:19 AM   #12
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Default Re: POS or NEG ground

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Originally Posted by 1930 coupe View Post
I do not understand why all the debate over POS or NEG ground.
The cars left the factory with POS ground and there is no need to change it.
I don't think the debate is pos or neg but rather having everything oriented one way or the other.
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Old 08-04-2013, 10:49 AM   #13
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Default Re: POS or NEG ground

I've also got to agree that PC/SR knows what he is talking about. I've run both positive and negative ground with the original generator. Keeping the generator polarized for negative ground is more trouble than it is worth unless it is rebuilt with NEW field coils and armature. If I changed to negative ground an alternator would be the easiest way. As for the coil, If I changed to negative ground, I would also reverse the coil polarity. With too cold spark plugs and a weak replacement generic coil , it will make a noticeable difference if the coil polarity is incorrect.. Whether the difference is large or small , I want the hottest spark. Good spark makes a difference in cranking, general performance and whether the plugs run sooty and the muffler collects unburned gas and backfires when shut down. I use the ignition coil and spark tester from Brattons, part number 17140. This tool shows if the coil is connected + or -. there is no risk of getting shocked and it works, no matter if you are running six or twelve volt.
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Old 08-04-2013, 03:17 PM   #14
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Default Re: POS or NEG ground

This my attempt to help make it simple and not complicated for those that are tripped up and frustrated about a simple subject, so rather than throw something tricky at you, I'm just asking questions to get you relaxed and in a logical thinking mode. And I'm not trying to set myself up as some kind of guru, because I'm not. Think about my questions and their answers, as I asked. jmeckel posted excellent answers I was looking for, except his answer on the mag, though correct for a Model T, is not correct for an A with, say, a Wico mag. I'll just give you the answer to that one: two plugs would constantly be firing pos ground and two would be firing neg ground. I would like for someone who runs a mag to post why that that is. Now, a couple more questions that jmeckel has alluded to: Why is the primary winding given its name? Why is the secondary winding given its name? How do these windings differ? If you are running, say, neg ground, which spark plug electrode will be negative, the center electrode or the outer electrode? If you answer my questions correctly, you will probably figure out why I made my original statement.
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Old 08-04-2013, 03:24 PM   #15
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Default Re: POS or NEG ground

I'd better ask the condensor question again because jmeckel gave a tricky answer. Which side of the condensor stores the electrons? Are condensors marked pos or neg ground? Why?
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Old 08-04-2013, 04:38 PM   #16
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Default Re: POS or NEG ground

This is so over the heads of most people why post it?
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Old 08-04-2013, 04:53 PM   #17
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Thumbs up Re: POS or NEG ground

Yes, the thread is a little over my head. But I like learning new things even if I don't understand all of it. I run a Delco-Remy {'35 Chevy truck} generator on my '31 "A". This Delco was normally negative ground. However, I'm running it Model-A style positive ground and it works great.

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Old 08-04-2013, 05:16 PM   #18
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Default Re: POS or NEG ground

Again, I'm trying to make this simple, not difficult. Here's another answer to a couple posts on this thread. Swapping the coil leads can't change whether the spark jumps from the plug's center electrode to the ground electrode or vice-versa. If the battery is connected positive ground, the plug's ground electrode will be positive and the electrons will have to jump from the center electrode. If the battery is connected negative ground then the spark plug's ground electrode will be negative and the electrons will jump from the ground electrode to the center electrode . Swapping coil leads will determine whether the current going to ground through the points passes through the primary winding or secondary winding and therefor how high a voltage is induced to fire the plugs. THIS IS NOT ROCKET SCIENCE. The battery current must pass through the PRIMARY coil winding and through the points to ground, so that when the points open and the field created by the 6 or 12 volts passing through the PRIMARY winding collapses, a high voltage(what should it be, 20,000?) will be induced in the SECONDARY winding which will then discharge across the plug gap to ground. It is the ratio of coil primary windings to coil secondary windings that determines the voltage available at the plugs. If you vainly attempt to change coil polarity by swapping coil leads, you will lower the voltage to the plugs. And that,folks is why the windings are named PRIMARY and SECONDARY. About all coils today have their low tension terminals marked (+) or (-). That confuses most people and it shouldn't. Back when pos and neg ground cars were intermingling, you would find coils with their terminals marked "BATT" and "SW" (for points). Today, since most all cars are wired neg ground, the semi-literate manufacturers label the coil terminals "+" and "-"., and therefor the "+" means primary and the "-" means secondary whether it will be used in a positive ground or negative ground system. None of the components in a Model A ignition system are polarity sensitive.
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Old 08-04-2013, 05:51 PM   #19
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Default Re: POS or NEG ground

Quote:
Originally Posted by Jim Huseby View Post
I'd better ask the condensor question again because jmeckel gave a tricky answer. Which side of the condensor stores the electrons? Are condensors marked pos or neg ground? Why?
The short answer is neither. It all has to do with opposing fields.

The molecules of the dielectric material are polarized in the field between the two conductors. The entire negative and positive charge of the dielectric is displaced by a small amount with respect to each other. This results in an effective positive surface charge on one side of the dielectric and a negative surface charge on the other side of the dielectric. These effective surface charges on the dielectric produce an electric field, which opposes the field produced by the surface charges on the conductors, and thus reduces the voltage between the conductors. To keep the voltage up, more charge must be put onto the conductors.
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Old 08-04-2013, 06:59 PM   #20
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Default Re: POS or NEG ground

Hello Mike V. I asked the condenser question in a way that could be treatad in the most simple manner in order to help answer the pos/neg quandry that unnecessarily agonizes and terrorizes many fordbarners. My intent is to take away the fear and terror and to demonstrate how simple my original subject is, and not to intimidate or alienate anyone. This is not a contest or demonstration of intellectual superiority. Discussions of break down voltage characteristics, inductance and resistance in a capacitor...well, we're just not at that level. All we need to know is that the condenser stores a charge. Now, the rest of that question was: is the condenser marked with a (+) terminal and a (-) terminal, and why?
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Old 08-04-2013, 07:16 PM   #21
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Default Re: POS or NEG ground

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Again, I'm trying to make this simple, not difficult. Here's another answer to a couple posts on this thread. Swapping the coil leads can't change whether the spark jumps from the plug's center electrode to the ground electrode or vice-versa. If the battery is connected positive ground, the plug's ground electrode will be positive and the electrons will have to jump from the center electrode. If the battery is connected negative ground then the spark plug's ground electrode will be negative and the electrons will jump from the ground electrode to the center electrode . Swapping coil leads will determine whether the current going to ground through the points passes through the primary winding or secondary winding and therefor how high a voltage is induced to fire the plugs. THIS IS NOT ROCKET SCIENCE. The battery current must pass through the PRIMARY coil winding and through the points to ground, so that when the points open and the field created by the 6 or 12 volts passing through the PRIMARY winding collapses, a high voltage(what should it be, 20,000?) will be induced in the SECONDARY winding which will then discharge across the plug gap to ground. It is the ratio of coil primary windings to coil secondary windings that determines the voltage available at the plugs. If you vainly attempt to change coil polarity by swapping coil leads, you will lower the voltage to the plugs. And that,folks is why the windings are named PRIMARY and SECONDARY. About all coils today have their low tension terminals marked (+) or (-). That confuses most people and it shouldn't. Back when pos and neg ground cars were intermingling, you would find coils with their terminals marked "BATT" and "SW" (for points). Today, since most all cars are wired neg ground, the semi-literate manufacturers label the coil terminals "+" and "-"., and therefor the "+" means primary and the "-" means secondary whether it will be used in a positive ground or negative ground system. None of the components in a Model A ignition system are polarity sensitive.

Well, kinda sorta. I understand you're trying to over simplify this. The condenser/capacitor is what really induces the secondary voltage and why the system won't work without it. But, I understand why you're saying it like you are. You're coming across as talking down to everyone, I don't think [hope] thats your intention.
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Old 08-04-2013, 07:24 PM   #22
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Default Re: POS or NEG ground

Quote:
Originally Posted by Jim Huseby View Post
is the condenser marked with a (+) terminal and a (-) terminal, and why?
No because it will fit only one way, simple enough?

You don't like the answers so you ask again?

So let me answer again in terms even you can understand;

It's the plugs that care about polarity not the coil!
The condenser is not marked because it can go in only one way.
NEITHER side "stores" electrons more them the other.

If you have A POINT TO MAKE, MAKE IT!!!

You were given simple answers and not so simple answers but neither is making you happy, WHAT DO YOU WANT???????
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Old 08-04-2013, 07:26 PM   #23
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Default Re: POS or NEG ground

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I don't think [hope] thats your intention.
I do! I think he gets off on treating the readers like idiots!
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Old 08-04-2013, 07:26 PM   #24
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Default Re: POS or NEG ground

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...You're coming across as talking down to everyone, I don't think [hope] thats your intention.
Gotta agree with that; if your intent was to keep this simple, I don't think it's working...
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Old 08-04-2013, 08:24 PM   #25
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Default Re: POS or NEG ground

I'm takeing it that way also.There is a correct way to connect the coil and its not any way that you choose. This will only be confuseing to people that don't know any better. This thread is silly and should be deleted.
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Old 08-04-2013, 08:33 PM   #26
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I'm sorry, but I'm the one that's simple-minded and humble. I did not offer to explain this subject for any other reason than to explain a simple set of facts in a gentle way. My intent was certainly not to lure anyone into a position for them to get themselves publicly embarrassed. I did set out a set of simple questions that would help, if you calmly and intelligently thought them through, but some of you took it as some kind of personal attack instead of an interesting exchange. Now, I will be considering withdrawing facts in order to stay friends. I like having friends, especially ones who can toss ideas around, even if they disagree, until the light bulb comes on, or not. Still friends. But I won't change facts. As I said, I'm no guru of any kind and don't want to get involved in a test of intelligence, which I would certainly lose. The subject I originally started has no emotions and is not influenced by emotions.
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Old 08-04-2013, 08:49 PM   #27
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Default Re: POS or NEG ground

are u from tennesee , too?
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Old 08-04-2013, 09:28 PM   #28
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Default Re: POS or NEG ground

"If the battery is connected negative ground then the spark plug's ground electrode will be negative and the electrons will jump from the ground electrode to the center electrode."

This is just flat wrong. Autos have had a negative ground systrem since the 50's and they fire through the center electrode, if wired correctly.
The coil does not care about positive or negative ground, only the direction of flow. Change the primary polarity connections and the secondary is also changed.

This can be tested easily. Take an analog voltage meter on highest setting, attach one lead to ground, the other to the plug wire, crank the engine and see which way the meter jumps. Reverse the coil connections, and the meter will jump the other way.

Last edited by PC/SR; 08-04-2013 at 10:58 PM.
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Old 08-04-2013, 10:18 PM   #29
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Default Re: POS or NEG ground

I would suggest everyone read this short piece about coil polarity by the Chicagoland MG club. It's the best explanation I've seen. It also gives a couple ways to test your coil polarity.

http://www.chicagolandmgclub.com/tec...neral/574.html
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Old 08-04-2013, 11:26 PM   #30
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Default Re: POS or NEG ground

GEEZ! "THEORIES" & CONFUSIONS abound!! It's a simple car, just hook it up for positive ground, hook up the coil properly, just like it left the factory & worry about something important, like changing the oil & greasing 91 fittings & oiling yo horn! Bill W.
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Old 08-05-2013, 05:45 AM   #31
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Uh oh. We're going to start an oil thread for horns ! Now ya done did it Bill !
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Old 08-05-2013, 07:32 AM   #32
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Default Re: POS or NEG ground

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GEEZ! "THEORIES" & CONFUSIONS abound!! It's a simple car, just hook it up for positive ground, hook up the coil properly, just like it left the factory & worry about something important, like changing the oil & greasing 91 fittings & oiling yo horn! Bill W.
Very well stated!
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Old 08-05-2013, 10:40 AM   #33
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Default Re: POS or NEG ground

Here's a nice wiring diagram that some good citizen posted years ago (sorry, I can't identify who deserves the credit.)




Here's a close up of the coil wiring.



The thinner wiring is the secondary winding. If the diagram were more accurate, there would be about 100 times as many turns of it as of the heavier primary wiring.

MOST IMPORTANT: Notice that one end of the secondary winding is connected to one end of the primary winding. This ultimately determines how the polarity at the coil connections determines which way the electrons will be going in the secondary (and in the spark plugs). Here's how--

The goal is to have electrons flow down the center secondary wire that goes to the plugs. BUT, the electron flow induced in the secondary windings will be of the OPPOSITE POLARITY (i.e., direction) as the current in the primary windings. Thus--if you focus on the junction point where the primary and secondary windings connect--in order to get electrons to flow FROM that point, thru the secondary windings, and then on to the plugs, the electron flow in the primary windings must to be TOWARD that point. And, it is that direction of electron flow in the primary windings that you determine when you connect the battery to the coil. The electrons will be going the right way if that primary/secondary junction point is connected to the positive battery terminal, and the other end of the primary to the negative battery terminal, from whence cometh the electrons.

Since that primary/secondary junction point is internal to the coil, you need some external marks to let you know what's what, hence the "+" and "-" notations commonly used. Of course, only one of these connections will be by an actual wire path that you can trace back to the battery; the other will go to the ignition points to ground and back to the battery thru the sheet metal, etc.

On a correctly wired, positive ground Model A, the "+" coil terminal must connect to the ground, or ignition points, side of the circuit. That is the red wire in the diagram. The "-" coil terminal must connect to the "hot" wire coming from the battery via the starter and the ammeter. That is the black wire in the diagram. On a negative ground car, the opposite connections would apply. If you have a coil whose terminals are marked something like "SW" (switch) and "CB" (contact breaker), rather than "+" and "-", you have to know whether that coil was for a negative or positive ground car.
I hope this helps.

Steve

Last edited by steve s; 08-05-2013 at 10:52 AM.
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Old 08-05-2013, 11:14 AM   #34
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Default Re: POS or NEG ground

When I commented that the schematic should have the + and - on the battery identified, I was neither advocating or condemning positive or negative ground on a Model A. I was merely pointing out that the addition to the schematic (a very good one) might save some confusion down the way for a less experienced Model A owner/restorer trying to wire his car as it came from the factory.

I wish I had as much spare time on my hands as some of you folks do.
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Old 08-05-2013, 11:53 AM   #35
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Default Re: POS or NEG ground

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When I commented that the schematic should have the + and - on the battery identified, I was neither advocating or condemning positive or negative ground on a Model A. I was merely pointing out that the addition to the schematic (a very good one) might save some confusion down the way for a less experienced Model A owner/restorer trying to wire his car as it came from the factory.

I wish I had as much spare time on my hands as some of you folks do.
I wonder where your comment is--I don't see it above.

Otherwise, retirement is a wonderful thing!

Steve
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Old 08-05-2013, 12:19 PM   #36
Mike V. Florida
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I wonder where your comment is--I don't see it above.

Otherwise, retirement is a wonderful thing!

Steve
This whole thing started from another thread.
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Old 08-05-2013, 08:00 PM   #37
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'Nice schematics, Tom and Steve. Especially of the coil. It looks like I stand corrected and publicly embarrassed myself. Nevertheless, thanks all for your frankness. I see that my mistakes were not looking at my own schematics and assuming that switching coil leads would force the primary and secondary windings to swap roles. Thanks for your clear explanation and for explaining that the high voltage discharge from the coil will be opposite the coil's low tension polarity. You can spank me, or use a ball bat.
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Old 08-06-2013, 05:03 AM   #38
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No problems Jim,

The superb quality of the sheet metal work that you do, and the honesty by which you run your business speaks for itself and by far outweighs any annoyance over you being mistaken on a subject which is anway regarded as black magic by 50% of model A owners.



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Originally Posted by Jim Huseby View Post
'Nice schematics, Tom and Steve. Especially of the coil. It looks like I stand corrected and publicly embarrassed myself. Nevertheless, thanks all for your frankness. I see that my mistakes were not looking at my own schematics and assuming that switching coil leads would force the primary and secondary windings to swap roles. Thanks for your clear explanation and for explaining that the high voltage discharge from the coil will be opposite the coil's low tension polarity. You can spank me, or use a ball bat.
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Old 08-06-2013, 11:40 AM   #39
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Default Re: POS or NEG ground

I learn here every day and have had "set" thoughts changed here as well.
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Old 08-06-2013, 06:38 PM   #40
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Default Re: POS or NEG ground

Admitting being mistaken is FAR less embarressing than sticking to your guns when you're wrong, just for the sake of it!

Well done!
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