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Ford 9N, 2N & 8N Discussion Forum
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Coil Hooked up Backwards...is it bad?

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Gino

11-05-2004 14:40:11




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Hi Guys, Iam having a tuff time starting the sidemount 6v, 8n. I hooked up the coil backward (ie distributor wire to negative, with Battery at positive ground), and also just found out the distributor wire was shorting. I reversed the coil polarities, but can't get anything out of the center coil wire. Any ideas? do you think my new coil is shot?? Thanks, Gino




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Dell (WA)

11-05-2004 17:50:34




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 Re: Coil Hooked up Backwards...is it bad? in reply to Gino, 11-05-2004 14:40:11  
Gino..... ....as a general rule its (+) to (+). That means iff'n your 6 volt battery (+) is connected to ground (and thats the way it came from the factory), then connect the ignition coil (+) to ground thru the the sidemount points terminal. Simple, eh?

I've been told you can loose upto -40% of your sparkies with incorrect coil polarity. I personally have seen -25% loss at ignition school when demonstrating incorrect coil polarity.

And NO, incorrect coil polarity doesn't hurt the coil, just the sparkies. And as a general rule, your 1-nipple roundcan ignition coil is fairly bulletproof.

Bottomline, when your ignition points are worn and corroded and your sparkies gap is worn wide and carboned, you'll have trouble starting. But then, you really need a tune-up with new ignition parts ennyways.

Iff'n you found your sidemount thru terminal shorted and you still don't gitt enny sparkies, guess what? your still shorted somewheres 'cuz you ONLY gitt sparkies when the points OPEN and iff'n yer points wire is still shorted the coil will NEVER make sparkies even iff'n you can see your point opening and closeing..... ....Dell, the self-appointed sparkie-meister

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Bruce (VA)

11-05-2004 16:54:15




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 Re: Coil Hooked up Backwards...is it bad? in reply to Gino, 11-05-2004 14:40:11  
On a positive ground system, the "+" goes to the coil. But, wiring it backwards should not prevent the tractor from starting unless you have other problems. Reversing the coil polarity will reduce the spark, but not stop it. Replacing the condenser & checking the point gap is a good place to start.



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Bob

11-06-2004 09:58:55




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 Re: Coil Hooked up Backwards...is it bad? in reply to Bruce (VA), 11-05-2004 16:54:15  
Actually, reversing the coil polarity DOES NOT reduce the spark. It just reduces the effectiveness of the spark. When viewed on a calibrated ignition oscilloscope, the peak-to-peak voltage will be the same, only with reversed polarity.

The loss of EFFECTIVENESS of a reversed-polarity spark is due to the fact that because of "thermionic emission" you want the leading edge of the high-voltage spark to the thermally HOT center electrode of the spark plug to be NEGATIVE with respect to the cooler "ground" electrode.

Obviously, this would have to do more with avoiding missfire once the engine is running, because from a cold start, there is going to be no thermal advantage to the center electrode.

Bottom line, with the coil hooked up properly, you should have a better RUNNING engine, but I can't see where it matters at cold startup.

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Bruce (VA)

11-06-2004 10:48:21




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 Re: Coil Hooked up Backwards...is it bad? in reply to Bob, 11-06-2004 09:58:55  
Whew! You are working some of my brain cells that have been dorment since Electronics 101 in 1966! Precision in the written word is important, and my post should have read: "reduce the effectiveness of the spark" instead of my shortcut approach of "reduce the spark". Frankly, all I could remember is that reversing the polarity causes the spark to fire from the ground electrode to the center electrode, rather than vice-versa.

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MikeT

11-05-2004 16:46:57




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 Re: Coil Hooked up Backwards...is it bad? in reply to Gino, 11-05-2004 14:40:11  
It might be the condenser.

Inside a round can coil, one side of the primary winding and one side of the secondary winding are hooked together. That's the side that needs to go to the distributor. BUT, there ain't no way to easily tell which side that is!

For most coils marked with a "+" & "-", that side would be the one marked as "-". Before negative ground systems came along, coils were marked with something like BAT and DIST or some such. The BAT terminal went to the battery regardless of polarity and the DIST side went to the distributor.

If the other side of the coil is hooked to the distributor, then the secondary winding will be firing through the primary winding, which will weaken the spark somewhat. There probably even will be a reverse secondary voltage induced in the secondary coil which wouldn't be good either.

Now, what I'm saying is to hook the "-" terminal of the coil to the distributor. But, Dell will be along shortly and probably say why you shouldn't do that!

Test it both ways and see which way gives a hotter bluer spark.

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souNdguy

11-05-2004 21:29:48




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 Re: Coil Hooked up Backwards...is it bad? in reply to MikeT , 11-05-2004 16:46:57  
I would still bet that if the coil was marked 'bat' and 'distribuitor', that the coil should be hooked up to whatever OEM polarity the tractor was.. for instance.. if the tractor was positive ground.. then 'distribuitor' would go to ground. etc.

Soundguy



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MikeT

11-06-2004 10:21:54




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 Re: Coil Hooked up Backwards...is it bad? in reply to souNdguy, 11-05-2004 21:29:48  
Check this site out.



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Bob

11-06-2004 10:18:58




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 Re: Coil Hooked up Backwards...is it bad? in reply to souNdguy, 11-05-2004 21:29:48  
S.G.,

That brings up a good point. The markings, "BATT" and "DIST" are MEANINGLESS on a coil unless there is a part number on the coil, or you are otherwise CERTAIN of it's original intended use.

A coil marked "DIST" and "BATT" originally intended for a negative ground system would be labelled directly opposite of a coil originally intended for a positive ground system.

I have several ignition oscilloscopes, and have more than once verified these differences in actual operation.

The interesting thing with the ignition 'scopes is that the actual polarity if the display is "flipped", so that the negative-going leading edge of the spark is display as RISING vertically, which makes it easier for the average mechanic to view the firing voltages of the plugs in firing order and relate them to each other, for troubleshooting.

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souNdguy

11-06-2004 13:20:08




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 Re: Coil Hooked up Backwards...is it bad? in reply to Bob, 11-06-2004 10:18:58  
My point exactly. You need to know the oem application of an individual coil if it is only marked 'dist/bat As the oem application will identify what ground polarity was intended.. etc. As for the other posters advice of just blindly hooking up the coil to bat and distribuitor ( as marked onthe coil ) without regard to polarity, IMHO is just shooting in the dark, with a 50% chance.

Soundguy

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MikeT

11-06-2004 13:59:13




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 Re: Coil Hooked up Backwards...is it bad? in reply to souNdguy, 11-06-2004 13:20:08  
Well, I think the "+" and "-" designations came about only after negative ground systems were well entrenched.

Like I said earlier, the post that is commonly connected to both windings inside the coil should go to the distributor.



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Bob

11-06-2004 14:23:22




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 Re: Coil Hooked up Backwards...is it bad? in reply to MikeT , 11-06-2004 13:59:13  
I have Delco coils from as far back as the 40's labelled (+) and (-).

There are Ford coils from the (+) ground 50's, and (-) ground 60's, 70's, and 80's labelled (DIST) and (BATT), and there's GOT to be a difference between them.

I believe the important thing is spark polarity at the plug, not which terminal serves as the common between the primary and secondary windings. The is such a difference in the turns ratio between the primary and secondary windings, and such a difference in wire gauge, and resistance (and impedance) that the difference there is all but negligable.

Most all the mechanic's references I've ever seen from the point era refer to the spark polarity at the plug as the determining factor in how the primary of a coil is connected into the circuit.

I have never been brave (or stupid?) enough to use the method often illustrated in the texts of holding a pencil with the point in the path of the high-tension spark, and observing which way the sparks fly. The ignition 'scope is a bit safer!

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8ngreenhorn

11-05-2004 15:19:49




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 Re: Coil Hooked up Backwards...is it bad? in reply to Gino, 11-05-2004 14:40:11  
My used 8N came that way. Dell stated it might only provide a weaker spark, but wouldn't harm it, but I'm very green when it comes to 'Ns.



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