12V Coil Question for Front-Mount Distributor

I inherited my father's '49 8N. (My grandfather
bought it new.) About 10 years ago, my
father converted it to a 12 Volt negative ground
system. All has been fine until this year.
It will run about 45 minutes to an hour, quit,
then start up when cooled. After reading in this
forum and talking with a gentleman who works on
tractors, it seems to be the coil.

I do not know whether the coil on on the tractor
is a 6V or 12V, although I think it may be 6V,
as the resistance from top connection to tab connection on bottom reads less than 1 ohm. I get no resistance reading from top connection
to pigtail conntection.

The voltage to the coil measured 12.32V. There
is also a ceramic resistor (not the ballast
resistor) that measures 1.5 ohms. I did not
see the ballast resistor. Where is it suppose
to be mounted? I'll double check.

Now for my question. When I replace the coil
with a new 12V coil, what resitor size, if any,
to I need to install?

I have read about 100 - 200 previous posts on
this subject. At least I educated myself enough
to know some questions to ask and measurements
to take, I hope :).

Thanks,
Allen

P.S. Sorry for the long post.

I can assure you that YES, your run for 45 mins is a typical frontmount coil failure.

I can assure you that your present coil is a 6 volt coil because the now available 12 volt frontmount coil is ONLY about 5 years old and was NOT available when your tractor was converted to 12 volts 10 yr ago.

The 1.5 ohms ceramic resistor, is indeed a 12 to 6 volt conversion resistor. And it is NORMAL to read about 12 volt at the coil terminal with the distributor points "OPEN". This also tells me that you do not have an electrical problem to the coil.

Your coil primary (tab) reading is correct, less than 1 ohm. Your secondary (pigtail springy thingy) reading should be about 7000 ohms, you need to change your ohmmeter range (otherwize it will read incorrectly), unless you have a modern digital meter (with auto-range). iin which case, no resistance is an OPEN winding and will definately cause NO SPARKIES.

The "infamous ballast resistor" is mounted on the backside of your dashpanel.

While the concept of a 12 volt coil and a 12 volt tractor system is good, you'd have to "re-wire" to make it work. If'n yer "electrially challenged", I wouldn't recommend the change over to 12 volt coil.

If'n it were me, I'd just replace your BAD 6 volt frontmount coil with new 6 volt coil, because you have a WORKING 12 volt conversion..... ....Dell, a 12 volt advocate for the right reasons

Thanks for the help. I have another question
regarding the placement of the ballast
resistor. Where on the backside of the
dashpanel is it mounted?

The reason that I ask is that the 1.5 ohm
ceramic resistor is mounted behind the
dashpanel near the oil pressure gauge.
I suppose that it is possible that the ballast resistor was removed. If so,
I will need to install another one.

Thanks,
Allen

Thanks for all your help. I got a new
6V coil, put it on, and the tractor started
immediately. I have not worked it yet. All
I do is a little light mowing.

By the way, I looked behind the dash just below
where the ammeter goes (it was replaced with a voltmeter) and did not see the ballast resistor.
Should I put one in or leave it as is?

Thanks,
Allen

Could be that the 12 to 6 volt converter resistor has also been sized to include the needed resistance value of the ballast resistor. Electronically, that is quite eazy to do, its hard to tell remotely. But if'n you really want to pursue the issue of "missing" ballast resistor, read the coil terminal voltage with points closed and engine not running. If you read about 3.5 volts (2.5 min, 4.0 max), yer good to go for 'nuther 10 years. And don't worry about your ballast resistor, its there somewheres..... .....Dell

I checked the voltage with points closed and
it read 3.62V, which is as it should be.
I didn't think the conversion was incorrect
but wanted to be sure. The gentleman that
converted it was a retired Lockheed employee
who trouble-shooted electronics on planes.
Unfortunatley, he passed away in March.

Thanks for all your help. I'm ignorant about
engines, etc. in general. I have learned from
you and this forum. Thanks.

Allen