12volt conversion... So confused...please help

Hi everyone...I have a 1947 8n that I inherited from my grandpa...My dad said it was running when he parked it in the barn 2 years ago....I am so confused as to this crazy 12volt conversion along with the wiring and this reducer or resister...Is there a way I can start from fresh and rewire it? It has a 12volt coil so can I just remove the reducer? My father just told me it gets a spark and then sometimes it don't...I don't understand the reducer that says 60volts down to 4.2 volts....I so badly want to get this tractor running to honor my granddad...He brought it brand new

It's called a resistor.

Technology & materials being what they were in the 30's, that square coil would melt if it ran on much more than 4 amps for any length of time. (see tip # 38 for an example). In order to get a hot spark at the same time the starter was drawing max current from the battery, a ballast resistor was added in the ignition circuit. What that did was add about .3 ohms of resistance in the circuit, added to the 1.5 ohms of the coil. That got you 3.5 amps or so at start up. As the voltage increased when the engine was running to about 7.5 volts, the resistor heated up, adding more resistance in the circuit. 1.0 ohms hot, plus 1.5 ohms of the coil got you down to 3 amps or so to keep from melting the coil. The same rule (actually, Ohm's Law) applies to a 12v circuit. I= E/R. Current equals voltage divided by resistance.

So, if you have a 12 volt coil, all you need is the resistor that came on the tractor from the factory.

As in the picture.

And no more resistors. (see tip # 30)

" Is there a way I can start from fresh and rewire it?"

Yes!

That is what I would do (see tip # 42)

First, tell us what type alternator you have. Or post a picture of it.

Once you know if you have a 1 wire or 3 wire alternator, then you order a new wiring harness from this site or nnalert's. (and order all the manuals too, see tip # 39)

Then, Google "wiring diagrams" JMOR and find the one to fit your tractor.

Don't forget to order a new OEM resistor (as in the picture) and battery cables too.

75 Tips

thank you so much Bruce

also see my post below on the wiring for a quick and easy wireing diagram, and it will use your ballast resistor.. etc.

I converted my 9n to 12 volt. With the second resistor in place tractor will not start. Without it it starts and runs fine. They say you need the second resistor to protect the coil. Do not know what to do.

(quoted from post at 11:18:13 07/09/14) I converted my 9n to 12 volt. With the second resistor in place tractor will not start. Without it it starts and runs fine. They say you need the second resistor to protect the coil. Do not know what to do.

Click to expand...

ounds simple enough to me. Run it with one & if coil goes bad, replace it with a 2.5 Ohm "called 12v" coil.