Super A electrical question

Anonymous-0 · Feb 16, 2009

All,
We are having a hard time starting our old tractor (will not turn over, could be battery but it goes through them pretty quickly), anyway I decided to try to figure out how this thing is wired. I found a couple of wiring diagrams on the net, one that represents a distributor ignition and one with a magneto. The magneto diagram does not show a coil in the system, while the distributor system does show a coil. Our tractor does have a magneto but there is also a coil mounted and wired in too. The wire from the magneto housing goes to the negative side of the coil. The tractor is also a negative ground (at least thats the way the battery is in there now), aren't these tractors suppose to be pos ground. Has the electrics on this tractor been modified or is this some hybrid factory set up and/or does the way this thing is wired make sense? The tractor runs fine when its cranked.

Thanks for any help
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Janicholson · Feb 16, 2009

All questions answered (I think)
A patch on a faulty magneto is to use a coil from a point and coil system to substitute for a magneto coil. (common bridge tactic 9or in some cases permanent non-elegant solution.
The points in the mag are used as points for the coil. It works, but is not the best.
A distributor (opinion) is probably the best solution. Next best is a good mag. (magman on this site, and others do rebuilds and exchanges of IH mags)
A distributor gives a RPM related advance curve fitting the tractor's engine. a Mag is either retarded for starting with the impulse coupling, or in full advance mode for running.
A mag with internal issues in the impulse coupling will not retard the spark, causing starting issues, and or running issues if set to start well.
A seperate issue is the charging system, and battery cables. This tractor needs single ought (1-O gauge) wire with soldered on ends. With lesser wires, it will crank too slow to start well.
John T Charging system check sheet is the best place to go for the charging issue checks. JimN

John T · Feb 16, 2009

Not much to add to Jims good info other then if its currently at Neg ground (even though if originally Pos ground) then the coil is wired correct if its little - terminal wires to the mags points as you indicate.....One problem when adding an external coil to an old mag n just using its points n condensor (sure it works) to switch coil current is the points may not last as long if the coils inductance is quite a bit different then the original magneto coils inductance cuz the condensor may not be the correct mfd rating..If the points seem to constantly build up a mound on one face opposite a pit on the opposite face the condensor isnt the correct size and a bad condensor can shorten the life of the points..

Bob M's wiring diagrams can get ya going other then a modified mag isnt exactly the same as a pure mag ignition or a pure coil ignition although they are close...

John T

ScottyHOMeY · Feb 16, 2009

Jim's got it pretty well covered. The wire from the external coil down to the distributor (the cap end of your magneto is a distributor) should be hooked to the pole of the coil marked the same as your chassis ground. The other pole of the coil runs back yo your ignitions switch just the same as if she had battery ignition right from the factory.

Curious as to whether the battery is 6 or 12v, and if 12 whether you have a generator or an alternator on it? In the days when 6v was common, so was positive ground. When 12v came along with the alternator, ground was conventionally switched to negative. My only thought bringing that up is that if somebody put a 12v battery in but left a 6v generator on, that might explain the charging issue.

If the genny/alternator are sized for the battery, then John T's checklist is a good way to start tracking down your problem. If it is 12v with an alternator, thene you will need to make a small variation in the wiring from that shown in the IH manuals. For that go to BobM's very excellent diagrams and look for the one that applies. I think #5 will be the most informative for that case.
To BobMs place

TractormanNC · Feb 16, 2009

If yours is an early one and still has the 6 volt generator with the cutout relay, replace the cutout with a voltage regulator like used on later ones. Your battery will last much longer.

Anonymous-0 · Feb 16, 2009

Thanks to all for the info: I was wondering since the tractor already has a modified ignition set up if I should just go ahead and change it over to a 12 volt system. And, is it possible and/or easy (or economically wise) to change the ignition over to a distributer type ignition and get rid of the magneto. I am more interested in getting use out of the tractor than keeping it 100% stock, although I would like to be able to change it back to original if I wanted to at some time. Sorry for all the novice questions, I know next to nothing about older ignitions,

Thanks again,
Roger

ScottyHOMeY · Feb 16, 2009

With what it sounds like you currently have (6v, negative ground, with an external coil to the points in a magneto), it will run fine. You'll have to mind the points as John or Jim pointed out, as the condenser in the mag is possibly rated differently than the one for battery ignition. (That may also be what's making it hard to start right now.)

As far as converting to 12v and battery ignition, at least from the economics of it, you'd have the cost of a good used distributor and an alternator, and a few odd parts (bracket and pulley for the alternator . . .)and a battery. If you think you might want to put it back to original at some point, for the same money or less you could put it back to original next week. I see rebuilt H4 mags going for $150-$220. With that and a good set of heavy battery cables, and a magneto (single-pole) ignition button, you could go back to negative ground, repolarize your generator, and be good to go.

Thats my two cents! Let us know how you're making out with it

roger_from_nc · Feb 17, 2009

Again I appreciate all the input. As someone pointed out (and this kind of makes sense to me), these tractors were intended to run long ours and therefore charging with a generator/6volt system would work fine. However, alternator charging/12volt may suit circumstances where the tractor is not used for long periods of time and/or is not run for extednded hours at a time. I'll wait a bit and see if I change my mind, but right now I'm leaning toward changing it over to 12 volts. I still don't know what would be the smartest though as to whether to get rid of the magneto (since it is obvious it has a problem (coil is patched in)) and swith to a distributor ignition or to have the magneto re-built.

Again, if anyone wants to add input I greatly value others opinions,

Thanks,
Roger

Janicholson · Feb 17, 2009

Find a distributor from a 4 cylinder farmall (most will fit, but one from a A B C SA SC 1XX 2XX with the small series 113-123-135 CID engine will work well. Then have Magman or others rebuild the mag if you want to put it back together stock. JimN

Super A electrical question

Anonymous-0

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Janicholson

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TractormanNC

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