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Discussion Starter #1
To All, I just bought a 48 8n Ford that has been convereted to 12 volts. Got it form a kid who inherited it and doesn't know anything about it, so he is no help. Got it home, fired it up and put it to work pulling stuff out of the woods. It ran for about 15 min. then just shut off. I checked, no spark from the coil. After waiting 20 min it started up, and drove it to the barn and replaced the coil. Gave it a complete tune up and was going to charge the battery and saw that the positive was going to ground. With all that said, I thought that when you change to 12 volts, you go to a negitive ground. I called the kid I got it from and he said he may have hooked the battery up backwards, so now I am really confused. I don't know if he hooed it up backwards or if it's correct. I have not switched it and it starts and runs fine. Any words of wisdom.
Thanks, NATTT
 

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Discussion Starter #4
Yes, I have done some research and the tractor came with a 6 volt system with a postive ground. From what I have been reading, when you upgrade to a 12 vplt system you change to a negitive ground. So I don't know. still looking for answers
 

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Kish JD 318/420/430
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The only thing that would be polarity sensitive is the starter and the generator alternator. Those do not like to wired backwards. Starter would most likely spin backwards, not sure about solenoid would engaged if wired backwards. The generator/ alternator might fry the diode/rectifier pack. So start with those for model and serial numbers for how they are hooked up.
 

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Discussion Starter #6
Thanks. If I know more about it's past, this wouldn't be a problem.
Thanks again.....Tim
 

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Starter doesn't care. It's not they type of electric motor that runs in reverse when you switch the polarity. It always turns the engine in the correct direction no matter which way it's hooked up.

How was it converted to 12 volts? What was installed in place of the original 6 volt generator and voltage regulator?

If they were replaced with a 12 volt generator and voltage regulator then it could be hooked up either positive or negative ground and you would just have to polarize the generator accordingly, and you would need to know if it is an "A" or "B" type of generator circuit.You can do a Google search on those terms (What is an "A" circuit generator, same for "B", and "How to polarize an "A" circuit generator", same for "B").

If the original generator and VR were replaced with an alternator, chances are that it has to be connected as negative ground.

If it has been running fine with the battery hooked up as positive ground and the battery hasn't fried or exploded, and it continues to maintin its charge, chances are that it''s got a 12 volt generator and VR and that it's properly polarized for positive ground so you can leave it alone. To be sure, I would measure the voltage across the battery when it's not running, should be around 12.3 or 12.4 volts, then measure it when it's running. If it's charging properly the voltage should be between 13.5 and 14.7 volts when it's running. If the voltage actually drops when it's running then that means that either the charging circuit isn't working or it actually still has the original 6 volt generator and VR, and they just stuck a 12 volt battery in it. In that case you should keep the battery on a charger when you're not using the tractor, or convert it to a 12 volt charging system.

The only thing that you need to reverse when you go from a positive ground to a negative ground system is the primary connections on the coil. It will still fire in either polarity but the spark will be a bit stronger when it's hooked up in one orientation vs. the other.
 

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close enuff works for me
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6 volt systems have positive ground,,,12 volt systems have negative ground , have done this to a ford 8n and a 1946 ford truck, Used a 12 volt battery and a chevrolet 12 volt alternator with built in voltage regulator( all the chevy alternators from about 1974 -1985 have the built in voltage regulators) and are relatively inexpensive.The original 6 volt starter can be used with 12 volts ,,it just spins a little faster ,which is a good thing.
 

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6 volt systems have positive ground,,,12 volt systems have negative ground
Usually, yes, but not always. You can have 6 volt negative gound systems and 12 volt positive ground systems, but those are less common.
 

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Discussion Starter #10
Starter doesn't care. It's not they type of electric motor that runs in reverse when you switch the polarity. It always turns the engine in the correct direction no matter which way it's hooked up.

How was it converted to 12 volts? What was installed in place of the original 6 volt generator and voltage regulator?

If they were replaced with a 12 volt generator and voltage regulator then it could be hooked up either positive or negative ground and you would just have to polarize the generator accordingly, and you would need to know if it is an "A" or "B" type of generator circuit.You can do a Google search on those terms (What is an "A" circuit generator, same for "B", and "How to polarize an "A" circuit generator", same for "B").

If the original generator and VR were replaced with an alternator, chances are that it has to be connected as negative ground.

If it has been running fine with the battery hooked up as positive ground and the battery hasn't fried or exploded, and it continues to maintin its charge, chances are that it''s got a 12 volt generator and VR and that it's properly polarized for positive ground so you can leave it alone. To be sure, I would measure the voltage across the battery when it's not running, should be around 12.3 or 12.4 volts, then measure it when it's running. If it's charging properly the voltage should be between 13.5 and 14.7 volts when it's running. If the voltage actually drops when it's running then that means that either the charging circuit isn't working or it actually still has the original 6 volt generator and VR, and they just stuck a 12 volt battery in it. In that case you should keep the battery on a charger when you're not using the tractor, or convert it to a 12 volt charging system.

The only thing that you need to reverse when you go from a positive ground to a negative ground system is the primary connections on the coil. It will still fire in either polarity but the spark will be a bit stronger when it's hooked up in one orientation vs. the other.
Sorry for the late reply, just been working late.
The tractor have been updated to 12 volts with a alternator, coil, and 12 volt battery. I believe thats all thats been done. After I got it home, the tractor ran for about 15 min. then the coil over heated and the tractor died. after it cooled off it started up and i drove it to the barn and tuned it up with new points, condencer, cap, pluges, coil, and wires. I switched the battery to negitive ground and it started and ran fine. I do have a couple of questions. With a negitive ground, does the wire from the alternator go to positive or negitive on the coil? Do I need a resister on that wire? If I do, does it go before or after the coil?
I plan to run it this weekend. I will let you know how everything turns out.
Thanks, Tim
 

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Does it have an alternator or a generator? What does the voltage across the battery terminals measure when it's not running and when it is running? If it was keeping the battery charged when it was hooked up as positive ground and you just switched the battery without doing anything else, then the charging circuit is not going to charge the battery and is likely to damage the battery.

The polarity of the coil should be such that whatever side of the battery is grounded should have that side of the coil going to the points, as the point is what grounds the primary windings of the coil in the ignition circuit. As to whether the coil should have a resistor in-line with it, that depends on what type of coil it is. Look at the new coil that you put in. It may say on the body of the coil "12 volt no resistor rezuired" or 1"12 volts resistor required", and that woull tell you since is the tractor has been converted to 12 volts. If there are no markings, disconnect the coil and measure the resistance across the two small posts. If it is around 3 ohms then it does not need a resistor in a 12 volt system, but if it measures around 1.5 ohms then it needs one in a 12 volt system but not in a 6 volt system.
 
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