12 V batt in M

Over ont he N forum, we use a a8n10306 dropping resistor when we use a 6v coil and 12v battery to keep the coil and points happy.

Light bulbs would be the next issue., then the charging system.

Soundguy

BIG JOHN has been putting a Hitachi #14231 alternator on several tractors in place of a generator under the hood. This alternator was used on 1978-79 Nissan 620 pickup with a 2 liter engine and a 1980 Nissan 720 pickup with a 2 liter engine. At NAPA it is part #2138130. The cost of a rebuilt alternator is approximately $50 + core (And they won’t take a generator as a core). The alternator is 4 1/2" in diameter and 7" in length and will go right on the original mountings on the tractor. Use an 8" x 3/8" bolt and some pipe for spacers. Being Hitachi means that it is METRIC. You will need to drill out the mountings to 3/8". The tension adjusting bolt is also metric thread. The alternator is a three (3) wire set up which can be converted to one (1) wire. There are spade connections labeled S & L and a BAT post connection. The L spade is for the idiot light and can be disregarded. Use a jumper wire from the S spade to the BAT post and you are good to go. The pulley is a split type that you can widen using a spacer (once again metric). You will need to use a disc type lock washer and some “Locktite” because there won't be room to reuse the split lock washer that comes with it. I was able to put the washer between the two pieces of the pulley to make it wide enough for my existing belt. There is a built in regulator and a resister to keep the battery from feeding back to the alternator. This is a sweet fit under the hood that he has used on H's, M's and W models, also Cubs and many others. I add the following from my experience:
Be sure to switch the polarity of the battery to Negative ground to avoid damaging the alternator.
Consequently, you need to switch the wires on the coil, if you are using a coil.
Use a plastic covered connection when you connect the jumper wire from the S spade
On a Farmall M, turning the bracket upside-down will allow the alternator to fit nicely inside the hood using the existing generator belt.

You can't leave the 12v hooked up with the 6v generator. If you run the engine with 12v you need a ballast resistor on the switch lead to the coil.

GOOD LUCK