Farmall M Overcharging Problem

I recently purchased a 1951 Farmall M and when I run it at faster RPM the ammeter pegs out to the Positive side. It is still a 6 volt, positive ground system. There is also a small bracket with a small porcelin piece fastened to the top of the horizontal distributor. This porcelin piece has two wires attached to it, one of which goes to the back of the coil. I"ve never seen a device like this on a "M" and I"m not sure what it is for. Can anyone out there tell me where to start to check to rectify the overcharging problem? Could the voltage regulator possibly be sticking. I"m a little electrically challenged and don"t quite know where to start. Any advise would be greatly appreciated.

(quoted from post at 21:57:29 07/30/09) I recently purchased a 1951 Farmall M and when I run it at faster RPM the ammeter pegs out to the Positive side. It is still a 6 volt, positive ground system. There is also a small bracket with a small porcelin piece fastened to the top of the horizontal distributor. This porcelin piece has two wires attached to it, one of which goes to the back of the coil. I"ve never seen a device like this on a "M" and I"m not sure what it is for. Can anyone out there tell me where to start to check to rectify the overcharging problem? Could the voltage regulator possibly be sticking. I"m a little electrically challenged and don"t quite know where to start. Any advise would be greatly appreciated.

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Do you know for sure that it is over charging? Pegging the needle may be normal with an alternator. What is the voltage at the battery when the needle is pegged?

What you described on top of the coil is usually a resistor used to drop the voltage so a six volt coil can be used on a twelve volt system.

Does the tractor have an alternator or a generator? If it has an alternator it is possible that the resistor is being used to keep the excite circuit of the regulator from back feeding the primary ignition system so the the engine will shut off with the switch. In that case the power would come from the ignition switch to the coil and then through the resistor to the alternator. If the resistor is just between the ignition switch and the coil, with no wire going to an alternator, then it is part of a twelve volt conversion.

Use a voltmeter to check system voltage just to be sure. Unless you can definitely see that you have a 6-volt battery with the + terminal connected to ground, I'd agree with Owen that you probably have a 12-volt conversion.

Hello again everyone, I appreciate your responses. I don't have electrical testing equipment so will probably have to take the tractor to someone to check out for me. I was thinking more about this situation after i posted this message though and i am suspecting that maybe I do have a 12 volt conversion in this tractor and the previous owner for some reason replaced the battery with a 6 volt battery as I know the battery was replaced just before I bought the tractor. I will try to check this out before I go any farther. It does still have a generator and not an alternator on it. Thanks for the advise, I will post what I find out. I just have a tough time with tractor electrical systems and all the wires on this tractor are the same color so can't really trace them very easy.

It sounds like it was at some time converted from 6 to 12 volts and therefore has an external voltage dropping (12 to 6) series Ballast Resistor so that the old 6 volt coil could still be used. It would have one terminal to the Ignition switch and the other to the ignition coil i.e. its in series between the switch and old 6 volt coil, it drops 6 volts leaving 6 on the coil HOWEVER IF YOURE NOW BACK AT 6 VOLTS IT SHOULD NO LONGER BE USED, the wire from the ign switch would now wire direct to the coil... REMOVE THE BALLAST !!!!!!!!!!!!!

Next charging, welllllll if it was converetd from 6 (originally Pos ground) to 12 votls, someone may have also changed it to Negative ground. (Hows it wired now?? which battery post is to the tractors frame, Pos or neg ????) If thats the case the ammeter leads would have to have been swapped otherwise it would register bass ackwards i.e show charge when its really discharing but show discharge when its actually charging ????????????

If the ammeter is wired correctly if you turn lights or ignition on when shes setting not running it should swing over to - discharge,,,,if it swings to + charge its leads need swapped side to side so it will read correctly.

Regardless if the ammeter is wired right to see if its charging, the battery voltage should read around 6.3 volts just setting but when runnign at fast RPM it should raise to 6.5 to 7 or so DOES IT???????? If you have no voltmeter see if the lights get noticeably brighter as you go from slow idle to fast RPM, if so its charging !!!

far as the ammeter it may just be wired bass ackwards.

John T

take a look at the serial number tag on the genny. if its a red tag, its a 12v genny. a black tag will either be an original 6v genny or it could be a 6v genny that was re-wired for 12v. a few of my tractors were converted years ago to 12v, a genny from an early 1960"s gm car was used, and they could either be hooked up as a positive ground or neg, even with the 12v genny. you can pick up an inexpensive volt-ohm meter from radio shack or your big box lumber store, prolly 20 dollars and that will get you a reading. pretty handy tool to have.

Hello again and thanks to everyone who posted a reply. I don"t own a volt/ohm meter but will have to invest in one. As I said, this electrical system really challenges my abilities. I did try putting a 12 volt battery in the tractor very briefly and it didn"t correct the problem. The ammeter just wiggled back and forth between 0 and full charge, very fast. So I have the 6 volt battery back in the tractor as it was. It is hooked up as a positive ground, and the tractor does have a generator and not an alternator. That other little porcelain thing fastened to the outside of the distributor did look like a ballast resistor but the wire coming into it and going out from it was connected to the same terminal, which made no sense to me, so I took the whole thing off and that still made no difference in the high rate of charging. The tractor still runs fine. When you turn on the ignition switch, the ammeter registers about a 5 to 10 amp discharge, until you start the tractor, then it goes to a high rate of charge and stays there. If you turn on the headlights, it will charge a little less but still about 15 amps according to the new ammeter. And yes, I am sure the ammeter is hooked up right. Keep your ideas coming as I would love to solve this problem myself and not have to haul the tractor to town to get fixed, it"s a long way! Thanks for all your ideas!

We really need to know what the charging voltage is. There might be nothing wrong with the system at other than an ammeter that is a bit more sensitive than most, as indicated by the amount of discharge with just the switch turned on.

The battery gets drawn down when the starter is used and will except a high charge rate for a period of time as it recharges. The amperage should drop down as the battery reaches full charge. As long as the charging voltage is no more than eight volts at the battery you should be alright. Closer to seven volts would be better.

A fully charged six volt battery should have 6.3 volts. 6.5 volts will charge the battery but it will take a long time. A tractor that is used regularly for more than short periods at a time will be OK with a charging system that maintains 7 volts. Much more than that and you will have to keep adding water to the battery. Tractors that get run less frequently and for short periods at a time will do better with a higher charging rate. The higher the voltage the quicker the battery will recharge. The higher the voltage maintained while charging, the more likely you are to boil out the water.

6 volt or 12 volt battery, which do you have.A six volt generator will run wide open on a 12 volt battery.

A volt meter is about 15 bucks (get a needle type) from Radio Shack. A good amp meter to check the one you have in it will be more (auto parts amp meters read more like 50 + and 50 -, so it will give a clear reading on just how much it is really charging. 7.2 to 7.4 volts is great. To check the amp meter, (they do get to reading high as they age) replace it with a new one using the same terminals as are connected now. JimN

Again, to all who responded, Thank You! I just wanted to post what the end result was. I finally loaded up the tractor and hauled it to the local Auto Electric shop in town that is the best around. They checked out the tractor and said that it has a 6 volt generator on it. It seems that at one time one of the previous owners at least attempted to convert it to either 8 or 12 volts, and they had tweeked the voltage regulator up so that it was putting out about 10 volts at full throttle. The tractor now, as I said, has a 6 volt battery hooked up to positive ground, so the technician just advised me to replace the voltage regulator with a new 6 volt regulator and I should be good to go. Thanks again for all the responsed, It has been a real learning experience for this electrically challenged guy!