Battery polarity wrong, 611B still runs?

Recently bought a Case 611B, rough shape but still runs, and it came complete with manuals. Now, the wiring diagram clearly indicates a positive ground system, but I found the battery connected negative ground. Yet the tractor still starts and runs and charges the battery. I can understand the old mechanical regulator getting its polarity reset on first use, and setting the polarity on the generator was a routine procedure back when we had generators. But every starter motor I've ever seen the inside of (at least hundreds if not thousands) was a permanent-magnet type motor. The remote solenoid doesn't care about polarity, so of course it's going to send power to the starter--but why does the starter not spin backwards and the bendix drive hold the pinion gear away from the ring gear? AFAIK only motors with field windings (either series or shunt-type) will spin the same direction if the polarity is reversed, and then only if it's reversed for both armature and field windings. Did Case use a field-wound starter motor? Or was there a version of the 611B produced with negative ground that's not mentioned in either the owner's or service manuals? They really didn't have to work that hard to confuse me, it just sort of comes natural, as Huck Finn said. Anyway, since it ain't broke, I don't plan to fix it unless someone has a very good reason to; there are plenty of things that do need fixing on it, including some major fabrication on the loader cross-brace. But this is bugging what's left of my brain (I did a LOT of drinking in the folly of my youth), and I'd appreciate any insight anyone might have. Thanks!

"AFAIK only motors with field windings (either series or shunt-type) will spin the same direction if the polarity is reversed, and then only if it's reversed for both armature and field windings. Did Case use a field-wound starter motor?"

Yes, true of most all vehicle starters.

Do a search for Delco Remy Operation and Maintenance Handbook DR-324. Go to starter motor section and it will explain why starter turns same direction regardless of polarity

Your tractor can run either polarity if properly configured. If converted to alternator and unless specially modified it requires negative ground.

"Anyway, since it ain't broke, I don't plan to fix it". I agree!

Starters are not motor with magnets but instead use electromagnet winding so be it + or - ground they spin the same direction

I purchased a CASE 610 B....great Tractor:

However ...the battery was POSITIVE Ground/Earth and the ignition (COIL) was wired for NEGATIVE GROUND/ EARTH. Starter worked fine either choice of ground. Engine originally was in a CASE 600 Combine. Engine started,not as well as it now starts, with COIL wired for Negative ground/earth. I'm to install an Alternator...thus my choice of Negative Ground/Earth. When COIL failed the discrepancy in incorrect Coil connection was identified.

Thanks for the info, that clears it up. Yes, I'm aware of the coil polarity problems also, and it may require a new coil to make sure it's right, as I cannot find any + or - markings on the one I have, and I don't have access to an ignition 'scope to check it that way. It has been replaced before, unless Case decided to paint that one thing only on the entire machine blue. My first thought was that someone stuck a Bosch blue coil, like we used for Volkswagen street rods on it, but Bosch never ever failed to put their logo or + and - marks on their coils. But any universal coil should do just fine on this low-compression motor, it doesn't need 60KV to fire it off or anything. BTW the other problem with reversed coil polarity is premature wear on spark plugs and breaker points, especially the plugs; the ground electrode will erode instead of the center which is more resistant. The condenser shouldn't care, I think they still use paper capacitors.

If you have a coil that you cannot identify the + or - polarity, a trick that I have seen is to use a lead pencil and hold it between the wire and the spark plug and let the spark jump through the lead and watch the spark flare towards the plug terminal (correct) or toward the wire (incorrect), be careful to hold the pencil by the wood, not the metaal eraser end.

Now that's a trick I never heard of before, I'll have to try it. Maybe with a pair of high-pot gloves, I've been nailed by more-than-my-share of ignition sparks, thank you!