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Discussion Starter · #1 ·
My neighbor bought a 1946 Chalmers tractor and it has been running fine until the battery was too weak to start (6-volt system). I checked the battery and it was dry. We filled it and I went to put it on the charger and noticed the PO had installed the battery reversed. Starter/gen lead on the (-) and ground strap on the (+). IIRC if the battery is completely discharged it will reverse polarize and work normally. He had the battery checked at Autozone but didn't tell them about it being reversed. They said they it was 29% capacity and fully charged it and it tested OK. I don't know if they charged it reversed and now he wants me to help hom put it back in and I don't know which way to hook it up without it shorting the 65 year old wiring. Any suggestions? Is he better off just replacing the battery (it is only 3 months old according to the date on it)?
 

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Used to see that happen every once in a while with the old 6 volt batteries. I've even done it on purpose to make a wrong battery fit in the hole in floor boards before. I always just complete discharged them and re-charged with proper polarity. Have to be careful about making sparks so be sure it is completely dead before connecting charger.
 

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I would suggest before you do any re-charging to look for a manual on the tractor online or talk to some other vintage tractor guys. A lot of old vehicles and tractors had 6 volt positive ground systems. I have a 46 ford pickup with the 6 volt positive ground system all original and except for the slow cranking and dim lights it works well. (If you can call that well) I have worked on many old tractors with the 6volt positive ground systems and we would always put on a Gm style internally regulated alternated with the pulley to match the tractor and go to 12 V negative ground. This works pretty well unless you wnat to keep everything stock for collectors sake.
 

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Discussion Starter · #4 ·
I would suggest before you do any re-charging to look for a manual on the tractor online or talk to some other vintage tractor guys. A lot of old vehicles and tractors had 6 volt positive ground systems. I have a 46 ford pickup with the 6 volt positive ground system all original and except for the slow cranking and dim lights it works well. (If you can call that well) I have worked on many old tractors with the 6volt positive ground systems and we would always put on a Gm style internally regulated alternated with the pulley to match the tractor and go to 12 V negative ground. This works pretty well unless you wnat to keep everything stock for collectors sake.
Wow! Thanks. I guess you're right, I need to research that. That would explain everything. I never heard of a positive ground system. I'll see if he has any manuals. Thanks again.
 

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my step dad has an old A-C tractor. very nice. blew my mind when I saw that positive terminal bolted to the frame. his charging problems turned out to be a burnt out "cut-out". looked like an old set of points.
 

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If it has a voltage regulator, see if it has either an "N" or a "P" stamped on it. The "P" could be a tip-off for positive ground.
 

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You say you don't know what polarity "they" charged the battery to. You can tell with a common digital VOM. It will show polarity of your voltage reading. If its + with the red probe on the POS terminal, its charged 'normally'. If it shows a - voltage with red probe to POS terminal, its charged for "reverse" polarity. Being a '46 model, it probably is a positive ground system but you can ohm out the charging system and tell for sure. After you determine if its a positive ground system, install the battery and obtain cables that allow you to install them as needed. (You don't have to do anything to the battery, just be sure its polarity is correct when installed)
 

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I bet it is positive ground (I ASSUMED that you knew) :eek: The ground cable terminal post is bigger than the negative cable terminal post.

I'll ask my son if his A.C. was positive ground.

When I was working on cars in my younger days, just about everything except GM was positive ground, then when the transistor radios came out and most all cars switched to 12 volts, they also changed to negative ground.
 
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