Converting H to 12 volt

I talked with a neighbor the other day and he asked me if I would convert his Farmall H from 6 volt to 12 volt. I said yes, as soon as it warms up a bit. Refresh my memory please. Change generator to alternator, change to negative ground, switch wires on the coil and it should be good to go, correct?? He didn't seem too worried about the lights. Thanks, Chris

Switch the wires on the ammeter too.

If it has a distributor and coil you will have to add a ballast resistor before the coil or switch to a 12 volt coil that does not require a resistor. You can also put some 1156 bulbs in the lights, they are inexpensive.

I haven't done it myself, but have heard others say it works. Turn the mounting bracket upside down, use the original belt. Alternator should tuck up nicely inside the hood, no need to cut a notch in hood. Should be a strong 1/4 inch space to place with.

willie in mn

That is close if you are using a one wire alternator. If using a 3 wire Delco or Hitachi follow the attached diagram. A incandescent dash lamp like a 194 can be wired in series to replace the diode in the ..excite.. circuit if desired.
6 to 12 volt wiring diagram

Be Sure to mount the alternator securely and properly aligned for trouble free belt life.

You'll need to match the alt pulley width to the existing belt. Sometimes the generator pulley will transfer over to the alternator.

A good place to connect the alternator output wire is to the wire that is on the BAT terminal of the regulator.

My first car was a 1965 Barracuda 12v.
It had a ballast resistor and means to bypass the ballast when cranking. Ask any old mechanic. They will tell you the old points and condenser ignition systems used a ballast and bypassed the ballast during cranking.
Many people on YT forget to bypass the ballast.

My 1950 Farmall C has a magneto.
So no need to change it..

Some may get by without bypassing ballast by using too small of a ballast resistor and burning the points faster.

My Jubilee has a large enough ballast, it has difficulty starting if I didn't bypass the ballast..
Good luck.

I recommend you research bypassing ballast resistor. .

Do what you want to do, but I'd just put the original pulley on a 12v generator and keep it simple. I did that on one of my Oliver 66s and the 77.

Good Morning good questions, here's my response:

1) An original 6 Volt battery powered Farmall H coil ignition (NOT talking a magneto ignition) would NOT have had any ballast resistor nor any ballast by pass when starting system.........

2) If its a magneto ignition, it doesn't use battery for ignition, so no ignition change required when switching from 6 to 12 volt

3) If its a battery powered coil distributor ignition you can EITHER add an external series voltage dropping (12 down to 6) ballast resistor before the old 6 volt coil and use it orrrrrrrrrr use a full true 12 volt rated coil NO ballast required.

4) For a battery powered coil distributor ignition if you switch from POS to NEG ground the coil leads would need reversed. IE Match the coil polarity to suit the ground be it original POS or newly converted for Alternator NEG ground.

5) Of course for an Alternator as most all are NEG ground you switch the battery to NEG ground in which case per above the coil leads need reversed PLUS the ammeter leads need reversed.

6) A One Wire alternators output would wire to the ammeters LOAD (NOT battery/starter) side terminal, thats where the BAT terminal on a VR or Cutout Relay would have wired before

7) Change light to 12 volt.

Im sure I missed something so hopefully the other fine gents here can add to this

John T

With a 12 volt battery the original 6 volt coil plus 1 1/2 ohm resistor with no bypass, or a direct 12 volt -no external resistor required coil should both operate the same as original 6 volt coil with 6 volt battery.

I've seen many conversions with resistor added in series with 6 volt coil that did not use a bypass. I have seen several 6 to 12 conversion kits that came with a resistor that was way too high in resistance thus causing starting problems. One advantage to direct 12 volt coil is it eliminates guessing about the resistor.

You asked about converting a Farmall H from 6 volt to 12 volt.

Here's step by step instructions on converting a Farmall M which should be the same as an H.
6V to 12V

My first car was a 1965 Barracuda 12v.
It had a ballast resistor and means to bypass the ballast when cranking. Ask any old mechanic. They will tell you the old points and condenser ignition systems used a ballast and bypassed the ballast during cranking.
Many people on YT forget to bypass the ballast.

Mornin good neighbor X2 Thanks for the good info on your old Barracuda, I had no idea what they used

FYI and others who may be unaware, SOME 12 volt cars and tractors indeed used a 6 volt coil with an external series voltage dropping (12 down to 6) ballast resistor PLUS a ballast by pass circuit when cranking which helped improve cold weather starting ...

HOWEVER The 6 volt H in question, nor MOST 6 volt tractors with 6 volt coils, did NOT of course use any ballast resistor and ballast by pass when cranking circuit.

For those 12 volt tractors that used a 6 volt coil plus ballast resistor and ballast by pass when cranking circuit, I prefer you keep them in place and use them which can improve cold weather starting

Warm here in S Central Florida yayyyyyyyy

John T

With a 12 volt battery the original 6 volt coil plus 1 1/2 ohm resistor with no bypass, or a direct 12 volt -no external resistor required coil should both operate the same as original 6 volt coil with 6 volt battery.

X2

Thats because a typical original 6 volt coil has a LV primary resistance of around 1.5 ohms so if its in series with a 1.5 ohm ballast resistor you get a 50 50 voltage divider so 6 volts drops across the 6 volt coil and 6 across the ballast yayyyyyyyyyyyyy life is good lol

Nice sparky chatting with you

John T

I bought my Jubilee already converted.
It would crank and most of the time not start until I stopped cranking, then the battery voltage came up and it would fire the instant the battery voltage returned to normal

I carried a spare ballast in my Cuda.
If the engine fired when cranking and stopped the instant I turned the key to run, it had a bad ballast.

My 1668 cuda was the same way.

All cars back in the 60's were wired to apply full battery voltage to the coil when cranking.

If you don't by-pass your ballast and it runs, someone installed too small of a ballast resistor.

I wish we had an old mechanic on YT to confirm the ballast was bypassed in the 1960s and some old tractors also by-passed the ballast.

My question to everyone, Why use a ballast resistor and a 6v coil instead of using a 12v coil that doesn't require a ballast resistor?

They cost the same on YT parts.

All that bypass Chrysler used was a wire from the solenoid to the distributor then when you let go of the key it goes through the ballast. No big deal to do a bypass with a solenoid to start it. If not then a bit more work.

Chrysler used the key in start position to apply 12v to other side of the ballast. 12v to coil.
I use a diode on my jubilee. The other side of the diode goes to the starter. No key, push button to ground to energize starter solenoid.

This is a ballast off my 1978 dodge aspen wagon.
By measuring the voltage drop across it and amps through it
Mr OHM says the ballast is 1.26 ohms when hot.
Less ohms if you measure it with an ohm meter.



Whoever wired my Jubilee used a 1.26 ohm ballast, same as chrysler used in the 1960 and 70s,
I have to bypass my ballast.

I noticed YT sells conversion kits with 0.6 ohm ballasts.

Using a larger ballast means less amps and parts will last longer.

Using a .6 ohm resistor may be why people think today's points are junk.

(quoted from post at 15:13:07 03/05/23) My question to everyone, Why use a ballast resistor and a 6v coil instead of using a 12v coil that doesn't require a ballast resistor?

They cost the same on YT parts.

Click to expand...

Some people prefer to not replace something that does not need replaced. Some people prefer the look of the OEM coil. Keeping the original coil also prevents future confusion if it should ever need replaced by a future owner. Future owner will most likely not look at the coil, just go to the parts store and ask for one for their tractor. They will get a 6V coil, which will burn out in about 10 minutes without a ballast resistor.

Coils start at $17.50 on this site. Ballast resistor is $5 on this site. So they do NOT "cost the same."

12v Coils start at $17.50 on this site, no ballast needed.
6v Coils with ballast start at $17.50 on this site.