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12 volt ignition coil on 6 volt Ford 641

F

FlatFenders

Member
I just discovered that somewhere along the line, someone put a 12 volt coil on my Ford 641. It is still a 6 volt positive ground tractor. It has always stared and runs fine and there are no performance issues. So why do I care? Just curious. I would expect the spark voltage to be about 1/2 what it would be with a 6 volt coil. If that is the case, perhaps someone "closed the gap" on the spark plugs to make it run as well as it does? "If it ain't broke, don't fix it" would seem to apply here.
What do you guys think?
 

Does the fine print on the coil say “for use on 12V with a ballast resistor “ ? What is the ohm reading across the primary terminals ?
 
Almost bet you have coil that if the writing is still there would have said 12 volt coil ballast resister needed or in other words a 6 volt coil
 
If you go to a New Holland/Ford dealer and ask the parts man for a coil for a 641, the coil he's going to sell you will say 12 volt. I bought a new coil for mine, 12 volt, starts and runs fine. There was only one coil offered for those tractors. The number has been superseded a few times. The last number, I got from Messick's website, was 87726663. Ron
 
If it runs that good I suspect it may have what's in reality a 6 volt coil.

1) If its labeled "12 volts for use with (or requires) a ballast resistor" its in reality more like a 6 volt coil and will work fine on a 6 volt tractor, with NO ballast.

2) If its LV primary resistance as measured between its two small + and - terminals measures around 1.25 to under 2 ohms it's in reality more like a 6 volt coil and will again work fine.

3) If it aint broke don't fix it lol

John T
 
(quoted from post at 15:16:44 03/19/18) If it runs that good I suspect it may have what's in reality a 6 volt coil.

1) If its labeled "12 volts for use with (or requires) a ballast resistor" its in reality more like a 6 volt coil and will work fine on a 6 volt tractor, with NO ballast.

2) If its LV primary resistance as measured between its two small + and - terminals measures around 1.25 to under 2 ohms it's in reality more like a 6 volt coil and will again work fine.

3) If it aint broke don't fix it lol

John T
Click to expand...
..and on #3, if you insist, you can in fact, fix it until it is broke! :(
 
If you buy a 12 volt conversion kit off this site it doesn't come with a coil and tell's you to keep the 6 volt coil.
 
(quoted from post at 12:46:36 03/19/18)
(quoted from post at 15:16:44 03/19/18) If it runs that good I suspect it may have what's in reality a 6 volt coil.

1) If its labeled "12 volts for use with (or requires) a ballast resistor" its in reality more like a 6 volt coil and will work fine on a 6 volt tractor, with NO ballast.

2) If its LV primary resistance as measured between its two small + and - terminals measures around 1.25 to under 2 ohms it's in reality more like a 6 volt coil and will again work fine.

3) If it aint broke don't fix it lol

John T
Click to expand...
..and on #3, if you insist, you can in fact, fix it until it is broke! :(
Click to expand...

And #4,"if it ain't broke, you ain't trying".(Red Green)
 
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