John Deere 50 electrical ?

My grandfather just bought a 50 and I went to look at it with him. It has a 12 volt system but I noticed it had a resistor wired in before the coil. Why would it have that if it has a 12 volt coil and distributor? Thanks for any info.

Some 12v coils have an internal resistor,while others require an external resistor like yours has.

James-The coil is probably original 6v and requires a resistor to get from system 12v to 6v ignition voltage.

OK I was confused because the coil had 12v on the side. What would happen if I take the resistor off and get a new coil?

The JD 50-730 starts on 12 volts ( 12 volts give you a lot better spark)and when you let off the starter button it goes back to the 6 volt mode so your 6 volt coil will not burn up. You can put a 12 volt coil on it, but starting it will be harder (I think)

all of those old Delco distributers are set up for 6 volts. If you change to a 12 volt system, you still can have only 6 volts going to the distributer or you will fry points and condensers very quickly. I have gotten away with a 12 volt coil with a resistor in front of it but I have found I get better performance and spark out of a 6 volt coil in this situation. If you wish to eliminate the resistor entirely, I would switch the system over to electronic ignition.

The reason it has a resistor ahead of the coil is so it drops 6 volts and leaves 6 volts for the 6 volt coil its using, otherwise the coil would overheat from excess current and the points would burn up prematurely. If it has a working ballast by pass circuit, while cranking the ballast is by passed which produces a hotter starting spark for improved cold weather starts.

Some 6 volt coils may be labeled "12 Volts for use with ballast resistor" and they mean just what they say USE A BALLAST otherwise the coil overheats.

It would NOT have a ballast if the coil were a true 12 volt coil, the ballast (drops 12 down to 6) is required for a 6 volt coil on a 12 volt tractor.

John T

You can get a new full true 12 volt coil and toss the ballast. However, if the tractor has a working ballast by pass circuit you get a hotter starting spark if you use a 6 volt coil plus the ballast.

John T

"all of those old Delco distributers are set up for 6 volts. If you change to a 12 volt system, you still can have only 6 volts going to the distributer or you will fry points and condensers very quickly. "

There were many distributors that came from the factory with 12 volt system. The points and condenser do not care if the system is 6 or 12 volts if it is properly configured.

Condensers see several hundred volt peaks during operation and have a breakdown rating of several hundred volts.

The points care about current, not voltage. Current is controlled by voltage and resistance so if you increase the voltage from 6 to 12
volts you add more resistance to maintain the same current. Either add a resistor or change to a direct 12 volt coil.

Direct 12 volt coils do not have a separate internal resistor, they have more windings on the primary which increases resistance.

Do a search for Kettering ignition system to see how the tractor ignition system works.

The other posts explain reason for external resistor, and that you tractor probably uses a start bypass to supply 12 volts to coil when starter cranks the engine which gives hotter starting spark.

Actually those Delco distributors are the same and dont care if its on a 6 or 12 volt tractor. The points and condenser are NOT specifically for 6 or 12 volt tractors either. The voltage withstand rating on either are wayyyyyyyyy higher then 6 or 12 volts anyway.

That being said, the points do care about how much CURRENT they are switching (typically limited to around 4 amps or less so points dont burn prematurely) and that depends on the voltage, coil, and any ballast being used.

Hope this helps

John T