Farmall M no start - convert to 12v or keep 6v?

Hi All,

Great news - after the amazing posts from folks on here we determined the Farmall M is, in fact, set up as a 6v system.

Now the fun part.

I need to redo all the wiring anyway and am not sure if the generator or voltage regulator work as they are wired goofy -> goofy wire description below...

Question is, I do not know if generator or voltage regulator are good - can anyone provide details on a quick way to check both (remember, tractor doesn't run)?

Also, who knows if the switch resistor is any good, or the starter - any simple way to check?

What about the ammeter? Simple way to check?

Lastly, I can get coil, plugs, distributor etc cheaply so not worried there, but if switch to 12v system need to change out the generator and starter, no?

So, question is, is it cheaper to convert to a 12v system or keep and fix as a 6v system?

Certainly checking components will aid in this question/answer, so if anyone knows how I can cross off things to check, please let me know.

Goofy wiring:

Ammeter is connected to voltage regulator battery terminal - correct

Voltage regulator generator terminal is connected to arm terminal on generator - correct

Voltage regulator f terminal is connected back to switch resistor - what the heck

Field terminal on generator is grounded to case - what the H*
 
There are a number of places for a wiring diagram. I have an A, and I made a new harness following the old
wires, one at a time. Your M should be similar. I would get an alternator, make it 12 volt, will start faster.
No need to change starter, but do not crank for extended periods of time unless you want to rebuild starter.
change bulbs in your lighting system to 12 volt, and you are good to go.
If you have a magneto for ignition leave it alone, It works independent of battery and is/was a good system. If it is battery ignition
make sure your coil is compatible.
Kris
 
Several considerations. Sounds like wiring is pretty messed up already pretty simple to wire alternator such as Delco S10, wiring diagrams available on site. Alternator can use existing mount by turning it over and drilling a couple holes. It will definitely start quicker. If you have lights and will use lights on equipment it is much easier to find 12 volt bulbs. 6 volt system will start tractor if large battery cables are used. With alternator and 12 volt you can use lighter cables and don't have to be in that good of condition. with 6 volt coil you will need resister(easy to find) or change coils. 12 volt batterys of decent size are easy to find, sometimes 6 volt not so much. I guess it is up to you, you may well put more into fixing generator and repairing or replacing regulator.
I have changed 2 tractors over to 12 volt and would never go back
 
It is very simple to get it running. Simply put in a 12 volt battery hook it up + ground for now and then run a wire from the negative post of the battery to the ignition side of the battery and try to spin it over. If it spins over pull the center wire off the cap and hold it about a 1/4 inch from the block to check for spark. If you have spark then in theory if you add gas it should start
 
A backup light bulb for a 12V Chevy from the late '50' early '60's will fit the original light bulb socket. Don't know the # for sure but think it might be 1156 (single element). I remember the tail/stop lite bulb's (double element) is 1157. 1157's have "offset" negative prongs while the 1156's prongs across from each other.
 
Hi Old,

Reading through your post and want to confirm my understanding of what you said.

You are saying to hook up the 12v with positive ground - correct?

Then take the negative lead from the battery and connect to the ? to see if it spins? I am guessing the starter?

Then if it spins, you are saying to take the distributor lead out and check for spark like you normally do when checking for spark?

In theory I understand, but I don't see how the ignition coil would be getting charge to check for spark if I only am cranking the starter.

If I hook up the entire system with a 12v battery then wouldn't I be running the risk of doing damage to other components that are 6v?
 
I am say hot wire it. Hook both battery cable up like normal and then run a wire from the non-ground side of the battery to the ignition side of the coil and test for spark. Being that it is 6 volts don't leave it hook up for very long or you can burn up the points but for testing a 12 volt battery will work just fine and to run it for say 10 minutes of so it will be fine
 
Hi Hayfarmer,

I am seriously considering just converying to 12v.

I looked for an older starter today at the junkyard - no luck.

Found several old 1/2 inch pulley 3 wire Ford and Dodge alternators but no older GM style systems. I know the GM one's are internal regulated but unsure of the older Ford's etc.

Here is my question, if I have 6v/12v internally resisted coil, new, then I do not need the ballast resistor, correct?
 
I agree.

Alternator will be cheaper than either a generator repair or replacement regulator and more reliable in the long run.
 
You want an alternator like from a 1980 Chevy pickup truck. 3 wire hook up which is easy. You can buy one form a place like O'Reilly's auto parts for around $50.
By the way no such thing as an internal resister coil there just wound for 12 volts instead of 6 volts. You want a coil that will say no external resister needed. With an alternator you also have to hook it up for negative ground or you will let the smoke out of the alternator
 
Gotcha,

Considering I have an internally resisted 12v/6v ignition coil, could I do the following:

•hook up battery to positive ground

•connect battery negative to ignition switch and ignition switch to starter (disconnect ammeter, generator wires etc)

•run a wire from negative battery terminal to 12v/6v ignition coil

Check for spark?
 
You should have to battery cables which you hook up and then if the ignition switch works turn it on if it doesn't hot wire it. you have to hook up the 2 battery cables or the starter is not going to work. As I said in another post to you there is no such thing as an internal resister in a coil they are just made for 12 volts or 6 volts in the way they are wound
 
Gotcha,

So then what is an ignition coil that is designed for 6v without external resistor and 12v with external resistor?

Does that mean it is designed for a standard 6 volt system (no external resistor needed) AND that it works with a 12v system if you have a ballast resistor which steps down voltage from 12v to 6v?
 
There is basically 2 types of coils. One is a 6 volt coil that can be use on a 6 volt system or a 12 volt system with a ballast resister in line. Or there is the true 12 volt coil that does not need a resister. Many companies used the 6 volt coils with a ballast resister by pass so the coil got the full 12 volts for a hotter spark for start up.

And yes a ballast resister by th way it work puts an extra load on the 12 volts to make it 6 volts to keep the 6 volt coil safe and the points safe
 
Hi All,

Thnks to the great responses on here, I put all new wiring in, as suggested, disconnected the generator and bypassed everything except the ignition and starter circuit, as suggested and worked out the issues.

Coil was shot - put a new coil on and she sputtered, wanting to start.

So tomorrow I am gonna get a ballast resistor for the 6v coil and a new Delco alternator and convert to a 12v system.

Any tips on the mounting of the alternator to have it fit under the hood without issue and align properly with the pulley?

Any suggestions on the correct belt length?

Lastly, since I will be hooking up the battery with the negative grounded and the positive running to the coil via the resistor w/ the negative on the coil now connected to the terminal on the distributor, I assume there should be no issue eventhough this is reversed of a standard 6v setup - correct?

Thanks again everyone!

One step closer to ye olde 47 Farmall M running again😀
 

And just to be clear---if you do go with the alternator, you will now have NEGATIVE ground! The procedures Old laid out were for troubleshooting purposes only, and because your tractor originally came with positive ground. Just wanted to mention that.
As mentioned, there are diagrams on this site telling how to wire up an alternator.
 
DO NOT REPLACE YOUR STARTER. A 12V starter on 12V really doesn't spin much faster than a 6V starter on 6V. The 6V starter has heavier wire in the field coils and armature, will handle more current than a 12V. Might be a good idea to have it rebuilt. The place I've used for alternator & starter work has just started advertising in Red Power Magazine in the last couple issues. I had them rebuild the starter on my Super H a couple years ago, it was supposedly rebuilt by the salvage yard I bought it from back about 1980, but the guy that rebuilt it a couple years ago said it was a crappy job years ago. When I installed it and hit the starter switch it SCARED ME! It spun the engine over three times as fast as before. Starter was spinning the engine faster than the throttle setting I start the engine at.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top