12 volt conversion on an M

WV Farmall · Apr 1, 2012

I recently purchased a farmall M and the owner had converted it to a12 volt system. I am having trouble getting the ammeter to show charge. I dont know if the wiring is correct either. Would anyone know where I might get a wiring diagram for this system. It has a motorola alternator.

Janicholson · Apr 1, 2012

There are many wiring diagrams if Googled. There are hundreds of different Motorola Alternators. We really need to know which one it is. Some have external regulators, some do not!
Two things that may help. Check the charging voltage at the battery (across the terminals) if the tractor is running at 1/2 throttle, there should be 14.2 to 14.8 volts. If no more than 12.6 volts, it is not working. If the voltage is there, the charging circuit is probably not running through the amp gauge. The heavy wire from the alternator needs to be hooked to the load side of the amp gauge (not the side hooked to the starter switch)
A second idea is to use a Hitachi, or Delco 10SI alternator.
The diagrams included show original schematics, and for a Delco or Hitachi.
The Hitachi alternator is from a 1986 Nissan Pickup. Its advantage is small size.
See archives for Hitachi diagrams and hookup. Jim
Wiring diagrams from Bob M

Bob M · Apr 1, 2012

Like Jim says there's several different possible Motorola alternator schemes: remote external regulator, mounted regulator, internal regulator, etc). Need to know exactly which Motorola alternator you have (backside photo would be helpful) before we can help with wiring.

As for testing system operation, again per Jim's suggestion measuring the voltage at the battery is the best test - problem COULD be as simple as a stuck hand on the ammeter.

mkirsch · Apr 2, 2012

Check to make sure the wire isn't running directly to the battery cable and bypassing the meter.

My recently-acquired Super M has a one-wire conversion on it, and the wire runs straight to the post on the starter switch. The ammeter always shows discharge because that's all that's going through it.

12 volt conversion on an M

WV Farmall

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Janicholson

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Bob M

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mkirsch

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