Tractor Repair: john deere m tractor, lead unit, ammeter

Question
QUESTION: I have a 1950{approximatly} john deere m.The battery is currently installed negative ground.Was it origionally positive ground? It charges but the ammeter reads backwards.I could swap the ammeter leads and leave it alone,but I would prefer whatever the origional configuration was.I am also not sure if the negative ground could damage or disrupt the generator or the regulator or whatever the two lead unit does.I think it is only some kind of cut out as the tractor ignition switch has two positions low and high charge.The operators manual states to only use high charge when you have used the starter or lights a lot or it will over charge the battery.I do not know if I were to reverse the polarity if the generator would need repolerised.I also wonder if my battery could be charged up backwards and sparks would fly if I hooked it up positive ground.I think the wiring is origional and that at some point someone just may have put the battery in negative ground by mistake- if it was positive ground to start with.Some say it will work either way,which makes me wonder why there would be different setups in the first place....

ANSWER: Hello,

  The info that I have found shows that the M was originally 6 volt positive ground.  If it is now negative ground, the ammeter will read backwards unless the wires to it are reversed.  The cutout is to prevent the generator from draining the battery after the engine is shut off.  Modern machines use diodes instead.  Instead of having a voltage regulator, the operator was the voltage regulator by using the high/low charge switch.  No, the battery can't get charged up backwards, and I doubt that the generator will need to be polarized, but I can't say for sure.  It probably did not do any damage to the generator or cutout but again, I can't say for sure and you will find out if it doesn't work after you get everything the correct way again.  Here is a link to a wiring diagram:   http://www.ytmag.com/jd/messages/306105.html

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QUESTION: I kind of like being the regulator,its part of the charm of this old heap.Thanks for the info.If you think it does not make any difference I may just reverse the amp gauge leads and leave it like it is, since I am replacing it with a new one anyway.I do not want to chance messing up the generator and such.I may need a jump sometime and negative ground is what most everything is anyway.Still,what was the advantage of positive ground in the first place? The generator has some three brush setup that charges 2 amp on low and 10 amp or so on high. Im not sure if all that works right any way but the origional setup.I have yet to check if it charges on low-the gauge dosn't move much.What would you do,change it or leave it?

Answer
I would hook up the battery the correct way which is positive ground, but that's just my opinion.  When jumping, it doesn't matter which is the ground.  As long as the jumper cables are hooked positive to positive and negative to negative it makes no difference.  People have debated for years what is the advantage of positive ground and everyone seems to have a different opinion.  My opinion is I don't think there really is an advantage, it's just a different way of doing things.