Coil (again)

This probably sounds stupid, BUT, I'll ask anyway. Why does the old 6v coil have batt. and coil on the terminals and my new NAPA 12v coil Has + and -? I understand + connects to the resistor, but it seems strange that - goes to the distributor. I assume since power to the distributor comes through the coil wire.? Just started tearing out useless 6v junk. A little intimidating tearing out wires from a somewhat running tractor. But hey, it's gotta be easier than say, a C5 Corvette.
 
You have a 12 volt conversion with negative ground right? So the minus sign on the coil would be wired toward the distributor where it will find ground through the points.
 

+ and - are relative. as your point of reference changes, so do they. u have a negative ground system. + is toward the power source and - is toward ground.
 
Did you get the NAPA IC14SB 12v coil I suggested? If so, REMOVE the resistor.

Coil polarity is supposed to match battery polarity. A positive ground tractor should have the positive terminal to the points. If it has a + sign, that's the side that goes to the points.

You now have a negative ground tractor, to the negative terminal goes to the points.

See tip # 33.

The small wire going to the coil from the battery and then from the coil to the distributor carries primary voltage, i.e., 12 volts in your case. The points switch that voltage on and off. When the points open, the magnetic field in the coil collapses causing the coil secondary voltage (22kv or so) to go through the big wire in the center of the coil to the distributor/rotor/plug wires and finally to the plugs where the gap there gives you a spark.


Worked that way since about 1911, I think.


Here is a better description of my 'Cliff's Note's" version!

https://en.wikipedia.org/wiki/Ignition_system
75 Tips
 
(quoted from post at 20:36:27 08/04/18) Hmmmmmm. I just got two opposite answers. Guess it wasn't as stupid of a question as I thought.
EALLY? Where do you see opposites?
 
Yes Bruce, I went to NAPA and got the exact one you said. What resistor do you mean to remove? The one that comes in the 12v kit?
 
You probably KNOW this but the distributor is not *powered*... The distributor interrupts the Coil Power, by removing and adding a ground at the proper moments.. So if the voltage is read during cranking on the wire between the coil and distributor, it would read either battery voltage or zero voltage...

IF the tractor has an ammeter, it will show more (or less) load when the engine is cranked during starting... depending whether the points in the distributor are opened or closed.......

When the points Open, the magnetic field in the coil collapses abruptly and that is when the SPARK occurs. When the points close again, the coil's mag. field builds up... (that happens much more slowly than the collapse.) Works well even in your "Belch-fire V8" turning above 6,000 RPM.
 
"Yes Bruce, I went to NAPA and got the exact one you said. What resistor do you mean to remove? The one that comes in the 12v kit?"

Side mount distributor, round can, true 12V coil, no resistor at all.
 
"Why does the old 6v coil have batt. and coil on the terminals and my new NAPA 12v coil Has + and -?"

An original OEM coil from a (+) ground machine would have the (-) terminal marked "BATT" and the (+) terminal marked "COIL".

An original OEM coil from a (-) ground machine would have the (+) terminal marked "BATT" and the (-) terminal marked "COIL".

That makes connecting a coil pretty much "idiot proof" when used on the original machine, but the connections will be backwards if the coil is swapped to a machine of the opposite ground polarity.

So, enter the generic coil, like the one you got from NAPA... by using a little knowledge and connecting whichever terminal matches the machine's ground polarity to the distributor, the coil can be used correctly on a machine of either ground polarity.

Clear as mud?
 

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