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Farmall M Wiring


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Hello,

I'm trying to re-wire my Farmall M tractor since some of the wires were broken or missing. I've studied several wiring diagrams but I can't find one that is exactly like my configuration. I'm posting four pictures of how I've attempted to wire it but I was wondering if someone could review the pictures and give me feedback before I plug in the battery

 

I've wired the positive terminal of the starter to the left side of the Start pushbutton switch (see the Start-Switch picture). The other side of the switch goes to the positive terminal of the battery and also to the ammeter box.

 

At the ammeter box (see the Lights-Ballast-Fuse-Ammeter picture) I've got the other side of the ammeter going to the positive terminal of the generator and also to the Run push-pull switch (red wires). The negative terminal of the generator also comes into this box and is wired to (I believe) the ballast (see black wire in picture)?

 

The other side of the Run switch goes to the coil (white wire of Run Switch picture). 

 

Can anyone see any problems with this configuration? Thanks for your help. Let me know if this doesn't make sense.

Luke

Generator&Coil.jpg

Lights-Ballast-Fuse-Ammeter Box.jpg

Run Switch.jpg

Start Switch.jpg

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I appreciate your response Snoshoe.

However, if I remove the black wire (which currently connects between the coil and the lighting panel/ammeter assembly) and route the white wire between the coil and generator, how will I turn off the coil once the engine starts?  Doesn't the coil wire have to route through the "run" switch?

 

I've been using the following diagrams for reference. As far as I can tell, none of them show any diodes.  The 12VoltAlternatorConversion diagram is the closest to what I currently have in place (generator, ignition coil, lighting/ammeter box, and NO regulator).

 

Do I need to move the top-left red wire (marked "To Run Switch") in the Lights-Ballast-Fuse-AmmeterBox photo to  the terminal on the right where the black wire (marked "To Generator") is located? That would keep the field side of the generator connected to the lighting box and then route it through the Run switch to the coil.

Sorry to be so challenged on this. I appreciate everyone's patience and guidance.

12VoltAlternatorConversion.jpg

12VoltNoCoil-NoRegulator.jpg

12VoltWithCoilAndRegulator.jpg

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In my experience, if you use a three wire alternator like the one you have and wire it through the push-pull switch with no diode in the system, when you shut the tractor off the alternator will back feed through your switch and keep the tractor running. You either need to add a diode in the wire from, think number 1 terminal on alternator, to the push pull switch (I believe, someone may correct me) OR use a true one wire alternator that self excites and run the main lug on the alternator straight to the ammeter, and from the ammeter to the hot side of the starter button. You will also have issues with battery drain the way its wired now. If you used a generic 4 post key switch that has ACC-OFF-RUN-START positions, you can use the 3 wire alternator and hook both 1 and 2 terminals to the ACC post of the switch. Then wire accordingly. I have done this on working tractors and it is a bit tricky to mount the 4 position switch on the letter series, and not original, but parts are easy to find. Sorry for the long winded response.  Just my experience. 

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On the first wiring diagram you posted, in that wire from number 1 terminal of the alternator to the switch it has a small light bulb, like a charge light. That's the diode snoshoe is talking about. In that diagram they use a small light bulb (there's a better name for it but I can't think of it?) In line to cut charge power off so it doesn't back feed. Some people use a diode. Either way you're going to need one in my experience or a) it won't charge b) it won't shut off with the switch or c) it will be dead because the power will back feed and drain the battery.  

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And also to add, I don't think the original wiring diagram is any use to you as far as the charging system goes. The light switch should have nothing to do with charging if you are using an alternator. Your alternator should be internally regulated and I would not recommend using the light switch. Again, just my experience. 

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Trying to simplify. I see the black wire running from light switch to number 1 alternator terminal. Don't need that wire at all. I see a white wire from (I assume stop switch) to coil. Adding a wire from that coil terminal to number 1 with diode between will work.

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Yes words don't match pictures. No black wire to coil either. I agree with everything wendyoaks said. Except I never thought of using an led. I assume it would work though. A wire from coil to alt is shorter therefore less potential problems. No light needed with ammeter but if led is cheaper or more available than plain diode why not.

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I just checked the posted conversion diagram. They are relying on a regular bulbs resistance to shut engine down. Wattage better be real low or it won't work. Substitute an led and it would probably be reliable. There are other methods using relays or switches with accessory terminals. The diode in the number 1 wire is what I used most on m's.

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I have used the 4 position generic key switches before with an alternator like that. I'd take the stock light switch out of the box and put the key switch in its place. Then run lights off separate switch. Dim setting was useless at this point in my opinion. As was the high low charge positions if so equipped. These were on working tractors. I can see the point if wanting  to keep original. 

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27 minutes ago, snoshoe said:

I just checked the posted conversion diagram. They are relying on a regular bulbs resistance to shut engine down. Wattage better be real low or it won't work. Substitute an led and it would probably be reliable. There are other methods using relays or switches with accessory terminals. The diode in the number 1 wire is what I used most on m's.

Just thinking. Led probably wouldn't let enough juice through to start alt.

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Thanks for all of the responses. Sorry about the confusion....I am using a Delco alternator (not a generator). I don't have a keyed switch...just the push-pull, on-off kill switch. 

Reading the above posts, I've got three more questions (sorry).

1. Does anyone have a part number, picture, or recommendation for where to get the diode for the number 1 wire?

2. I'm a little confused on black/white wire recommendations. If I understand correctly, I should remove my white wire and connect the black wire directly between the alternator and the coil. If I do this, do I still need the diode? Since I've bypassed the kill switch, how do I turn off the tractor?

3. If I remove the black wire from the lights/ammeter box, do I still have a complete circuit to charge the battery while the tractor is running or do I have to use a key-switch to utilize this box?

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6 minutes ago, SI Super M said:

If I understand correctly, I should remove my white wire and connect the black wire directly between the alternator and the coi

Leave the white wire alone. Remove black wire completely. Add wire from white wire on coil to number 1. Almost any diode rated 30 volt or more will work. Check Amazon, eBay or radio shack.

 

15 minutes ago, SI Super M said:

If I remove the black wire from the lights/ammeter box, do I still have a complete circuit to charge the battery while the tractor is running or do I have to use a key-switch to utilize this box?

That's what the wire you're adding is for. The diode is what allows you to shut tractor off

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Since you are using an alternator, the only wires going to the light switch need to be power to the switch and the wires going out to the lights. Other than that, don't hook anything charging related to the switch. Follow the first diagram you posted exactly. 

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The way you have it wired would actually work. You would have to turn light switch on for alternator to charge. Then when shutting down you have to turn light switch off to keep from draining battery.

I hope I'm not being to confusing.

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2 minutes ago, snoshoe said:

The way you have it wired would actually work. You would have to turn light switch on for alternator to charge. Then when shutting down you have to turn light switch off to keep from draining battery.

I hope I'm not being to confusing.

Would it depend on which switch he has though? There were two switches, one with low and high charge plus dim and brights (4 position) and one with just off, dim and bright (3 position)?

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To the OP, you're not eliminating the push pull switch by removing the black wire. Snoshoe is saying to move the wire that is on number 1 terminal of the alternator to the positive side of the coil and add a diode. That's where it can get power from to excite the alternator. Since the positive side of the coil hooks to the push pull switch it will still shut the tractor off, but only with a diode in the wire to number 1 terminal.

To simplify, remove black wire from light switch and take the end of that black wire and hook to positive side of coil. That looks to the the one butt connected to the white wire on number 1 terminal of alternator. Add a diode in that wire. 

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2 minutes ago, wendyoakscubs said:

Would it depend on which switch he has though? There were two switches, one with low and high charge plus dim and brights (4 position) and one with just off, dim and bright (3 position)?

Yes he has the 4 position switch and is connected to the wrong resistor. It will NOT work. Also your posting while I'm typing. So I'm just going to stand down unless asked specific.

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1 minute ago, snoshoe said:

Yes he has the 4 position switch and is connected to the wrong resistor. It will NOT work. Also your posting while I'm typing. So I'm just going to stand down unless asked 

My apologies snoshoe. Typing thoughts as I think of this. 

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1 minute ago, wendyoakscubs said:

My apologies snoshoe. Typing thoughts as I think of this. 

No problem. I don't want to add to the confusion. You obviously know what's happening here and I didn't notice the second resistor till you asked.

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10 minutes ago, snoshoe said:

No problem. I don't want to add to the confusion. You obviously know what's happening here and I didn't notice the second resistor till you asked.

You probably know more and have done way more conversions than me. Just been down this road a few times. If wiring through light switch on the right stud will work then definitely would be the way to go. 

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Diode, LED panel light, or incandescent light. All interchangeable for the purpose of exciting the alternator. Diode is the most compact and easy to hide under the hood. Having an "idiot light" on the instrument panel (I removed the light fuse and put an LED panel light in its place) is kind of cool.

You need to provide power to get the alternator to charge. Once charging the power is no longer necessary. That's why the light goes out. Having it on the light switch works too, but it's an extra step to remember and will likely lead to a few dead batteries. Using the diode/LED/light eliminates the step and is automatic.

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