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Farmall & IHC Tractors Discussion Forum

Farmall M - 12v conversion questions

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Author  [Modern View]

07-31-2020 21:15:11

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Hi All,

Worked out the details on the old model M and have decided to convert to a 12v system.


I know many say the Delco 10SI alternators are an option, but is hood modification needed? If yes, how so? Any bracket tips?

Seems a 10si would be a pretty tight fit so here are some other options, would like to know your thoughts...

What about a 40 amp kubota 3 wire alternator? https://www.discountstarterandalternator.com/p/new-alternator-kubota-thermo-king-12v-40-amp/
It is smaller, still internally regulated, and has internal fan?


What about a chevy mini 40 or 50 amp alternator? https://powerparts360.com/chevy-mini-alternator-denso-street-rod-race-3-wire/?gclid=EAIaIQobChMI88y4yY356gIVz8DACh3ZRA3mEAQYAyABEgKv7PD_BwE&gclsrc=aw.ds
Again smaller than a 10si, also internally regulated and internal fan?

Aside from brackets, and the other obvious parts I will change (coil, resistor, wiring etc) any little tricks/tips or common mistakes to watch out for?

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08-01-2020 08:22:22

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 Re: Farmall M - 12v conversion questions in reply to ChampagneNBeer, 07-31-2020 21:15:11  
10SI will fit in just fine with no cutting of the hood. It is a tight fit but it can be done

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P. Coltrane

08-01-2020 07:56:36

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 Re: Farmall M - 12v conversion questions in reply to ChampagneNBeer, 07-31-2020 21:15:11  
I think some kits come with a Hitachi alt.

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08-01-2020 08:08:34

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 Re: Farmall M - 12v conversion questions in reply to P. Coltrane, 08-01-2020 07:56:36  
Yep,most kits I've seen advertized do use Hytachi. They also come with 'bracketry','some' wire,'idiot light',other stuff. And cost around $200.00.

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08-01-2020 07:11:51

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 Re: Farmall M - 12v conversion questions in reply to ChampagneNBeer, 07-31-2020 21:15:11  
I have adone a dozen or so convwrsions in the last 15 years.The first,a SuperM,has had ZERO issues.Always starts and charges as it is supposed to . The last one(8N Ford) was done last summer.It also works as should. Easy.Here's how. First,COMPLETELY strip out the old dilapidated harness. Then go buy a one wire Delco alternator. . turn the lower bracket upside down. bolt the alt to the front ear. One bolt to one ear is enough.Or you can make your own bracket.Then run one 10 gage wire from the alt to the amp gage. Then from the amp gage to the battery cable at the starter. Then pull power from the amp gage to the ignition switch,then to distributor.14 gage is fine for that. Done.Wrap the whole thing in black electrical tape into a neat clean 'sanitary' harness. If you want/need lights,pull power from gage also.The 'tricky' part is the new belt. Find an old belt. Cut it and wrap it around the pulleys. makw a mark where the ends meet. Measure that and you have your belt size.Done.Easy/peasy. Of all that I have done,none have failed to charge at first start. None have experienced power drain when sitting for a prolonged period of time.If you want more info,call me. 9704171178. Steve

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08-01-2020 08:04:31

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 Re: Farmall M - 12v conversion questions in reply to DeltaSteve, 08-01-2020 07:11:51  
You will need to either replace coil,or use a resistor. Yes,it will run with the 6v coil,but not long,or will burn up points. My wifes SuperC,it ran less than an hour till it litterally smoked the coil.A 'universal' 12 coil from NAPA fixed that.Other tractors have run longer,but eventially all needed to have coils replaced. Like said,New 12v lights will be needed.I just use 12v 'tractor lights'. I usually always discard the old(iffy) rotary light switch and replace with a good push/pull light switch. Use appropriate fuses.I dont care weather or not if it looks "factory",It just needs to work. Reliably.As I said above,Wrap the whole thing in a neat clean sanitary harness. Use plenty of tiedowns to secure to the tractor. It should last your lifetime. Or atleast the life of the tractor.

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08-01-2020 04:54:17

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 Re: Farmall M - 12v conversion questions in reply to ChampagneNBeer, 07-31-2020 21:15:11  
Dad converted his '51 M from 6v to 12V Delco 10si alternator, close to 40 years ago. A tractor that struggled to start on 6v, oversize high compression pistons, live hyd pump, engine driven power steering pump, it JUMPS to life now. I use Sears Group 65 Gold batteries, close to 1000 CCA, find a 6V battery anywhere near as powerful. There's enough room around the alternator I can slide my hand between it and the hood. I REALLY hate guys that fire up the gas ax and cut up their hoods to install an alternator. Absolutely NO NEED to cut up the hood, Dad put a 10si on my Super H a couple years after the M. It's tight on the SH, but I can get my fingers between the hood and alternator. There's instructions somewhere on this website, think the lower mount has to be turned upside-down, and modified, maybe shortened? The voltage regulator needs to be removed, changes made to wiring, 6v coil replaced with 12v. All light bulbs replaced with 12v bulbs. Amp meter can stay, but you may need a higher amperage meter, most generators top out at 15 amp, alternators can run 60 ramps. The instructions tell how to install a diode to prevent power from running from the battery to the alternator, Dad didn't do that, We've just disconnected the battery ground cable as soon as we get off the tractor. The battery on the Super H I replaced a couple years ago was TWENTY years old, battery in the M was in the tractor when I hauled it here 14 years ago. Do a GOOGLE search on "Changing a FARMALL M from 6V generator to 12V alternator". Bet you get lots of articles to read.

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08-01-2020 04:34:17

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 Re: Farmall M - 12v conversion questions in reply to ChampagneNBeer, 07-31-2020 21:15:11  
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Someone will be along any minute to answer your question about hood modification. In the meantime, I'll contribute that either of those alternators look fine for your needs. The reason people got into the habit of using the 10si is because they were everywhere back in the day. Western Auto used to sell them for under $20. And sometimes you could use a half-off coupon. Ah, the good old days.

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08-01-2020 04:32:31

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 Re: Farmall M - 12v conversion questions in reply to ChampagneNBeer, 07-31-2020 21:15:11  
Quoting Removed, click Modern View to see

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