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Farmall & IHC Tractors Discussion Forum

Farmall M 12v electrical system

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01-06-2007 08:42:18

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I have inheritied a Farmall M tractor. It has 12 volt ignition and starter and will run. There was an old Delco Alternator mounted but not connected. The Battery is hooked up for positive ground. I bought a new Alternator but before hooking up I figured the ignition being wired for Pos Ground would burn the Alternator up imeadiately since the Alternator Case and is the same physical potential as the tractor body. I am going to assume i can reverse wire everything to work in a negative ground format. Do I need a different starter? Does the stter work either way? If not can it be rewired internally etc.?

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01-06-2007 12:33:34

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 Re: Farmall M 12v electrical system in reply to Ponderosa, 01-06-2007 08:42:18  
third party image

here ya go

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01-06-2007 10:48:05

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 Re: Farmall M 12v electrical system in reply to Ponderosa, 01-06-2007 08:42:18  
John T says it well but gets long winded. Alternator has to be - ground. Starter doesn't care if + or - ground and will spin the right way not matter how you hook it up. Also you need to make sure the coil is wired + to the ignition switch.

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John T

01-06-2007 11:40:23

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 Re: Farmall M 12v electrical system in reply to old, 01-06-2007 10:48:05  
Meeeeee Long Winded lol

Take care "old" friend

John T

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01-06-2007 12:40:49

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 Re: Farmall M 12v electrical system in reply to John T, 01-06-2007 11:40:23  
Yep once in a while you do carry on just a little much for us simple folk. But you do explain it well. I jsut figured I would put it in simple terms. I sort of said the same thing you did but I gve it short and sweet.

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01-06-2007 09:37:42

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 Re: Farmall M 12v electrical system in reply to Ponderosa, 01-06-2007 08:42:18  
Not sure what you mean the tractor has a 12 volt ignition and starter. Most with the 12 volt conversion use the stock 6 volt starter and ignition with either a 12 volt coil with internal resister or a resister ahead of the coil. There is a 12 volt wiring diagram for the conversion in the archives done by Bob M. I used it when I converted my SMTA to 12 volts and many others here have done likewise. It should be negative ground. The starter will work fine on 12 volts, Don't crank the engine for too long with it. If you get a 3 wire delco alternator an follow Bob Ms diagram it should work fine.

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John T

01-06-2007 09:25:34

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 Re: Farmall M 12v electrical system in reply to Ponderosa, 01-06-2007 08:42:18  
Ponderosa, Sooooooooo many questions so little time lol lets start with the basics.

1) Most allllllllll alternators including those Delcos require NEGATIVE GROUND PERIOD so I wouldnt try n wire it up at Positive ground whatsoever. i.e. hook the batery up with its - post to frame ground and + to starter/switch BEFORE you install n wire the alternator.

2) The starter will still work fine n turn the same direction REGARDLESS OF POLARITY i.e. if you convert to neg ground to accommodate the alternator NO PROBLEM with the starter.

3) Assuming its the standard points n condensor battery powered coil ignition NOT an electronic ignition (which IS POLARITY SENSITIVE), it will work at EITHER polarity buttttttttttttt the coil works best if its wired to match the polarity i.e. if at Neg ground its + gets voltage from the ignition switch and/or any ballast while its - wires to the distributor. If at Pos ground reverse that with - getting voltage from switch/ballast and + to teh distributor.

4) In the event you need to change from pos to neg ground the ammeter leads need swapped or else it will read bass ackwards. It will work at EITHER polarity but if you change things the leads need reversed.

5) If youre at 12 volts the coil must be a full true 12 volt rated coil or rlse if you use a 6 volt coil it needs an external series voltage dropping (12 to 6) ballast resistor wired in after the switch and before the coil.

6) Many people use the GM 10 SI internaly regulated 3 wire 12 volt alternator wired n configured to work like a one wire unit, post back if you need wiring instructions.

Hope this helps, post back any questions

Ol John T and all in Indiana

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