Old farm tractor electrical

The patient: 1956 Allis-Chalmers WD-45 farm tractor with the wide front end. Electrics presently: 6 volt positive ground. I would like to convert to a 12 volt negative ground. Tractor has no lights. The system has an electric starter, coil and points ignition and it’s a 4 cylinder gas engine. I think that all I need to do is put a resistor, such as the Chrysler-type ceramic block resistors and reverse the wires on the coil. That’ll keep the coil from frying. I think that I can just leave the distributor with its single wire alone. Am I right here? The 6 volt generator would be changed out to a Delco or small foreign car 12 volt alternator. The whole system then would be a 12 volt negative ground system. Am I missing something? The charging system is controlled by a relay mounted on the generator. I also have an amp meter where I think that I can just reverse the wires on for neg. grounded system. I can remove the relay by using a Delcotron or other alternator with the built-in regulator of the alternator. Am I right on this? Thanks,–Prof. Handy.

It sounds like you have most things covered. However, I would change the coil to a 12 volt unit if you can get it to fit in. Most block resistors are meant to reduce 12 volts to 9 volts. So if you get one you have to be sure that the voltage is dropped to 6 volts for the existing coil. Also, the starter is going to spin like crazy with double the voltage so be careful about sustained cranking because the starter windings and the solenoid will be heating quickly. In fact you might change over to a 12 volt solenoid to limit the current through the windings.

Keep us appraised of you progress.

I would think that the starter could be rewound to work better with 12 V if it becomes necessary.

There is no solenoid on this thing. It has a rod that goes down right to the top of the starter. It has a pivot pin in the middle of a cam-type device. When you pull on the rod, the rod then pulls on the pivoted cam. The pivoted cam then pushes on a large, round button which, in turn, puts large, copper terminals into contact with each other. (A copper trapezoid on the end of the button and its attached 3.8" shaft that contacts two copper terminals on the top of the starter). Think old-time foot operated starter systems. Instead of a foot, the pull rod does the pushing. Got you thoroughly confused about the push-pull thing? Anyway, a few old timers and a couple of younger guys have told me that as long as I only crank that starter for like 5-8 seconds, then let it cool for 3 minutes or so, then I shouldn’t have starter damage. This engine starts pretty well after about 3-5 engine RPMs. (Block heater set on a timer gets it going pretty well in the coldest weather). As I understand it, all coils are 6 volt. That’s why they use a by-pass circuit to get the engine turning, a full 12 volts directly to the starter. Then when you disengage the starter after the engine is running, they use an in-line resistor of some kind, a ceramic block resistor, an in-line fusible-link type mechanism, etc., to drop the voltage through the coil to 6 volts. So I think that I have that part covered by using a ceramic-encased resistor. I don’t have a conventional key-type ignition. The starter wire runs directly from the battery to the starter terminal as explained above. I have a push/pull (there I go again, eh?) on/off switch that controls the juice going to the coil. So, if my reasoning is right, an in-line resistor should work o.k. One that is set somewhere between 6-8 volts. As I stated in my original post, it presently has a 6V generator, the old three brush type with that 3rd adjustable ring for controlling output. I’ll just swap that out with a 12V alternator. Gee! I might even hook lights up! I’m just checking with you all just to make sure that this old brain is still working kinda logically. Thanks for all of your comments. It gives me food for thought in case I missed something or if someone might have a better idea.

Based on the info you supplied it sounds like you have it covered. I know the “Ballast resistor” for my 1969 Dodge dart drops the voltage to the coil from 12 volts to 6 volts after ignition so one of those should work well. I would recommend however that you carry a spare. In 20 years I have replaced three in my Dart usually at the worst possible time. As far as the starter it should operate fine on 12 volts as long as you avoid extended cranking. When and if it burns up you can have it re-wound for 12 volts.

I think you would not want to reverse the wires on the coil. The coil doesn’t care about positive or negative ground, just that the ground side is the ground side. Other than that, you’ve pretty much got it covered.

Oh, are you sure this is positive ground? My father used to have an old Ford with a 6V system, but it was negative ground. I don’t know about A/C tractors though.

Some DC motors change direction with polarity… You might bench test it just to be sure.

Let’s step back here for a moment and do some “out of the box” thinking. Is the whole purpose of this electrical upgrade to add 12V headlights? For a machine that old, I have to wonder if the conversion would be worth the effort. Can you obtain 6V headlights, such as from a vintage car parts supplier? J.C. Whitney might be worth a look. Do you think this tractor might ever end up as a collector’s piece? If so, extensive modifications might hurt its value. That’s generally true of vintage cars. If you want just 12V headlights, I would think that the lights wouldn’t care if it was positive or negative ground (although the alternator might). Are you planning to add other 12V electrical equipment?

Good point, I see the OP did not mention the starter, which would surely need to be replaced or modified in some way so as not to run backward and also for the higher voltage, though that might not be a big problem.

You can get 6V lights at farm supply stores.

I think MrPhil is right. What would really be cool would be for you to get the 6v headlights, if not from J.C. Whitney or Warshawski’s, then look in Hemmings Motor News at any place that sells a lot of magazines- hell just look up what you want and split. Personally I find their website a little disapointing. They always want you to get a subscription in order to get good info. Anyway w/the $/effort you’re going to put

out for the completion of this project, why not just leave it 6v; spruce it up; and send us a foto? But I guess you just like the tinkering part of it. To each his own. By the way, when you reverse polarity on a ‘71 Chevy C10 P-U starter it still rotates the same direction-FYI. Most 12v cars’ coils run on about 9-10v- did you pick up on that in Researcher’s post? That’s what 12v batteries drop down to during cranking;

any that would drop to 6v would be kaput or undercharged, and of course they probably wouldn’t have enough power to crank engine fast enough to begin with. You sound like you might be from up North- Canada, maybe? If so, then the feasability of your project is starting to make more sense- you could put a plow on front of tractor, hook up block heater the night before a snow storm, plow drive/lane @ 5:30 AM, then jump

start any non-cranking “automobiles” w/your 12v tractor/invention; and your neighbors’, too. Heck, why not go whole hog and wire up two 12v batteries in parrallel to make one super-high amperage 12v batt? Go for it , Prof, and keeep us posted!

No, I’m not from Canada. My grandparents were and all moved to Southern NH (Nashua-Manchester area) or Northern Taxachusetts (the Lowell area). I’ve lived in the middle of Colorado, in the middle of the Rockies since 1979 at 8,868 ft. above sea level. I’m going to upgrade to 12V just for simplicity’s sake. It’s a lot easier and less expensive to buy batteries and, when needed, to get replacement 12V alternators than it is to get 6V components. The starter presently has a battery cable running from the negative post of the battery to the main threaded post on the starter. The positive battery post goes to ground thus a positive ground system. All of the juice runs through the tractor frame. Circuits are completed by the juice running through whatever electrical component, such as the coil or starter, and then returns to the negative side of the battery. This thing does have a rear blade that spins 360 deg., a small front bucket and the bucket can be replaced with a 7’ regular plow blade. Both front and rear systems are hydraulically controlled by way of two separate hydraulic systems. The rear system was built into the tractor. Through some fairly ingeneous mounting of a hydraulic pump, the front part ( using a Massey-Ferguson up and down and tilt for moving the front bucket to dump or changing the scraping angle for the blade), the darned thing works really well. I got the tractor with this front system already modified and installed. I upgraded the front hyd. pump for more ‘guts’. The original system had a dinky little pump running off of the power take off. Not enough RPMs and not enough guts to lift a bucket with a full load of dirt. I found a double grooved belt pulley and modified it by attaching this double pulley with 3 hardened bolts to the front of the crankshaft pulley. I found a smaller diameter double belt pulley and mounted that to the front shaft of the pump. Now the front hydraulics work a lot better with a heck of a lot more guts. Now there’s no stopping me. This tractor has moved whatever amounts of snow Mother Nature has dumped on us and we’ve had a couple of 5,6,and7 foot storms within the past 10 years or so. My 1/2 yard bucket scoops up gravel and dirt pretty well, too. That’s why I’m trying to simplify the electrics by going with more readily-available 12V components. I will heed your advice about carrying spare resistor blocks. I happen to be using one right now (and for a bunch of previous years) on my '71 Chevy van w/ in-line 6 cyl. engine. When the original in-line resistor died, I simply cut out that resistor and replaced it with a Chrysler Corp. resistor block. It might be awhile before I get around to changing over to 12V because guess what? We’re in snow season right now and I’ll need the ‘wacky tracky’ to move that snow. (The tractor is painted yellow and orange, thus the ‘wacky-tracky’ handle. a.k.a.: Lee’s carnival tractor). I will keep you apprised of how this works out when I get around to it. Thanks, Y’all, for the input. I’m keeping this tractor for as long as it, and/or me is still alive. If I croak first, then it’ll be someone else’s chore to figure out what to do with it. Someone up in these parts will want to use it as I have.