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I recently acquired a 1942 John Deere A with a 12 volt starting system that needs re-wired. Does anyone know of or have a complete tractor wiring schematic that includes the starter and alternator circuits? Any help or knowledge would be appreciated!
 

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A wiring schematic for a Model A, I don't have. An internet search may provide you one. If you have a 1942 tractor with an automotive style alternator and twelve volt battery, then it was converted by a previous owner. Factory would have been a generator and six volt battery. The auto industry changed from six to twelve volt in 1955. Tractor manufacturers followed.
 

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John Deere A Wiring Diagram

"Does anyone know of or have a complete tractor wiring schematic that includes the starter and alternator circuits?"

Reviewed the Service Manual Electrical Systems SM-2029 under Section 80 ELECTRICAL WIRING Group 5 WIRING DIAGRAMS, TRACTORS on pages 80-5-1 and 80-5-2.

Take a look at the 6-Volt Starting Equipment diagram below.
6-Volt Starting Equipment.jpg

Since you have a "John Deere A with a 12 volt starting system", then the system will be a NEGATIVE ground rather than the original positive ground.

We have a 48A with a 12 volt system with an alternator.

Take a look at the simple illustration below of the alternator wiring.
Alternator Wiring.jpg
Take a look at the photo of the alternator.
Alternator.jpg

Take a look at the photo of the ammeter.
Ammeter.jpg

Take a look at the exciter switch.
Exciter Switch.jpg

Since your tractor has an ignition switch starter instead of mechanical pedal starter, disregard the starter in the above image.

Take a look at the 6-Volt Lighting Equipment diagram below.
6-Volt Lighting Equipment.jpg

Hope this helps.
 

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