Wartime H getting an upgrade

My brother and I decided to switch the
FFA's 1943 H to 12v before it gets
auctioned off next week. We order the
alternator from this website but it didn't
come with instructions or the electrical
connection for the alternator.

We odered mounting brackets from Steiners,
but they won't be here until tomorrow.

Does someone have the wiring diagram for
this 3 wire alternator? The tractor has a
magneto. We are trying to figure out what
to do with the 2 prongs.

Thanks in advance

The "S" prong goes directly to the big terminal with the "B" on it. The "L" prong goes to a voltage source to start the alternator. Choice one is a oil pressure sensing switch from NAPA or? It should have two terminals and close when it senses 5psi or so. This is "T"ed into the oil pressure usually where the pressure gauge attaches to the block with a 1/8th inch pipe nipple and a "T". The two terminals are connected to that L prong, and to the load side of the amp meter. When the engine starts, the oil pressure closes the switch and exciting voltage goes to the L terminal.
The second way is to put a push button momentary contact switch on the dash/light bar. It is connected the same way one terminal to the L terminal, and one to the amp meter load side. when it starts, the operator pushes the button one time to start the charging.
The output terminal can be connected to the amp meter load side with 10 gauge wire. The other wires can be 14 gauge. I like to put a heavy duty fuse in the circuit between the alternator out put, and the amp meter that is rated for 5 amps more than the alternator. (I think that alt is about 35 amps) Jim

The third way is a simple diode in the wire running to the L prong. You can even get prewired alternator plugs with the diode already installed if it's a Delco 10SI. Don't remember where but I've seen them.

IMHO, the oil pressure switch is too complicated and the push button is too much of a kluge.

There's a guy named Charlie Uthke, makes a simple diode assembly that clips into that top. Very economical, works great on my Delco 10SI at least. THis name and address are a few years old. But .... Charlie Uthke, Charlie's Repair, 22195 State Hwy 56, Austin, MN? 55912 [email protected]

I created a YouTube video start to finish of how I did my installs of the magnetos on my M, H, John Deere A, and Case SC. I have included the Farmall H video below. Also, a picture of the wiring diagram I have that I saved from Bob M's archives. The last photo is the wiring diagram I made referencing Bob M's. For the on/off of the alternator, I used an oil pressure switch from NAPA. You can also use a toggle switch (but to clean things up I prefer the oil pressure switch). It is a simple switch, one wire in, one wire out. Photos included of that as well (switch mounted on my Case SC, but is installed in the same fashion under the hood on the H).

Any more questions, please let me know!







1942 Farmall H Episode 9: 12 Volt Conversion

With a mag there is no need for a diode or resistor or lamp there is no connection to the ignition to keep it running, so it is not needed. Jim

I was told it is necessary to have the resistor/lamp in order to prevent voltage from feeding back into the alternator so that you don't burn up the fields in it? (I'm not that electrically savvy - just did what I was told I needed to do, LOL).. I

Not needed. The source of voltage (push button or oil switch) supplies voltage to the Alternator on the L terminal it appears to be (but is not) a ground that is sufficient to cause the charge light to glow if there is one (in this case none) as soon as the alt detects voltage at that terminal, it tries to charge putting voltage in the rotor. as the engine turns the alt that magnetism starts making more volts than the battery, and the L terminal changes to alt output. this means that there is 12v positive on both sides of the circuit and the light goes out. (in this case there is just nothing happening) If it had points and condenser distributor/coil ignition, and the ignition was used as the source of "exciting" voltage, the the 12v coming from that L terminal would keep it running after the key was shut off. The ignition system is shut off from this undesirable condition by putting a diode or lamp or resistor in the circuit. Jim

Gotchya! Well. I guess my tractors are set up 'in case' I decide to switch to distributor ignition, then! I have been told distributors run a little smoother. I just like the simplicity of a mag (and ability to run without battery).

The "S" and "L" prongs on this alternator are not labeled. One is vertical and the other is horizontal.

Thanks!