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John Deere 40 12V Conversion

J

johndeeregreg40

Member
I am converting my John Deere 40 to a 12V system. It doesn?t seem that difficult however, I keep reading that a ballast resister should be installed when keeping the 6V coil unless you have a magneto. Do I have to install one or does the 40 have a magneto and therefore it is not needed.
 
AFAIK, 40's all used a distributor.

Adding a ballast resistor is no big deal, other option is to replace the 6 Volt coil with a "true" 12 Volt coil, such as a NAPA IC14SB.
 
"[b:654c4848f0][i:654c4848f0]<font color="#6699ff">Do I have to install one[/i:654c4848f0][/b:654c4848f0]</font>"

Yes.

Take a look at the photo below.

a267559.jpg" width="650"


"[b:654c4848f0][i:654c4848f0]<font color="#6699ff">or does the 40 have a magneto[/i:654c4848f0][/b:654c4848f0]</font>"

No.

Take a look at the photo below.

a267560.jpg" width="650"


Hope this helps.
 
YES I agree with the fine gents and sparkies below, on a 12 volt tractor you can EITHER use a full true 12 volt rated coil orrrrrrrrr a 6 volt coil PLUS an external series voltage dropping (12 down to 6) ballast resistor. It simply connects in series between the ignition switch output and coils input as James indicated. The coil should be wired to match the tractors polarity.

That being said, a ballast is cheaper then buying a new coil.

The ballasts available at Tractor Supply or Rural King or NAPA etc. should have the same approximate resistance of your 6 volt coils LV primary (as measured between its + and - terminals) resistance so there's a 50/50 6/12 voltage divider created, and for typical old farm tractors that use a 6 volt coil that's approximately 1.4 to under 2 ohms.

John T
 
I was just looking over your setup and I was wondering what the red wire goes to on your alternator. I see the blue wire goes to negative terminal. And positive terminal and ignition switch go to ballast resister.
 
"[b:654c4848f0][i:654c4848f0]<font color="#6699ff">I was wondering what the red wire goes to on your alternator.[/b:654c4848f0][/i:654c4848f0]</font color="#6699ff">"

Take a look at the photo below.

a267596.jpg" width="650"


The red wire is connected to the ammeter.

Hope this helps.
 
I would recommend the coil Bob mentioned. I've always seen ballast resistors as a fire hazard. Probably just me being quare but all that heat and the chaff a tractor collects is something I prefer to avoid.
 
Approx the same as the 6 volt coils LV primary resistance for a 50/50 6/12 Voltage Divider. For many old farm tractors that's in the 1.4 to under 2 ohms range.

John T
 
That's a good system that was used on several makes n models of tractors. It helps extreme cold weather starting.

John T
 
If you are going to make the conversion, I am looking to buy a 6v serviceable gen to fit on a 40. I think the volt reg is still on it so all I need is genny. I would have a full set of 12v bulbs that direct fit the lights to get rid of/trade. Yes, I am going back to 6v so ring gear doesn't get ruined so fast. Give it a thought Long distance shipping could queer the deal. George
 
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