Ford 12v conversion

Restoring 62 Ford 4000 4cyl gas. Has a 12v electrical system conversion. Has a coil that says 12v - use with external resistor. Reading I"ve been doing says use external ballast resistor with 6v coils in a 12 volt system, don"t use with 12v coil . I"m confused... can someone smart about this tell me the real story, pls. The tractor ran fine before and I don"t want to hose it up by ignorance.

there are 12v coils with and without the built in resistor. as your states use with external resistor, you should have one on there. zip on over to napa, tell em you want an ignition ballast resister for a early to mid 1970's b-body chrysler product. about 5 bucks or so, porcelain looking deal with 2 terminals on it.

You MUST use a ballast resistor with that coil. WHY would you think they would print that information on the coil if a resistor were not required?

Fact is, a "12 Volt coil" labeled "use WITH external resistor" is actually a 6 Volt coil.

The reason for using a coil such as that is to aid in starting. When the battery voltage is drawn down by the starter during cranking, spark voltage is reduced.

By using a 6 Volt coil, a "positive temperature coefficient" ballast resistor or a "starting bypass" with a fixed resistor can be used to give full battery voltage to the coil during cranking, then dropping the voltage off as the PTC resistor heats up over the first minute or so after the ignition switch is turned on, or, in the case of a "starting bypass", it drops out a soon as the starter is no longer activated.

I'm NOT familiar with your specific tractor and how it was set up, or if that coil is original, but the fact remains you MUST use a resistor with that particular coil.

Steve, I agree with the other fine gents, do JUST AS THAT COIL SAYS i.e. USE AN EXTERNAL VOLTAGE DROPPING (12 to 6) BALALST RESISTOR otherwise the coil will get too hot and the points will burn up prematurely.....

Coils labeled "12 volts" or "12 volts NOT for use with external ballast resistor" are just as they say and indeed full true 12 volt coils no ballast required... HOWEVER ones labeled "12 volts for use with (or requires) ballast resistor" are in reality 6 volt coils and need the ballast just as they say....

The reason such coils are used on 12 volt tractors is because when cranking especially at low tems where cranking is hard n batetry efficieny is lowered there may only be 9 to 10 volts or less left available at the coil resulting in a weak spark when a good spark is needed the most.....BUTTTTTT if you use a 6 volt coil and by pass that external ballast ONLY WHILE CRANKING you get a better starting spark, then when she starts the voltage dropping n current reducing ballast is back in the circuit so teh coils is at the right current n temperature and the points arent switching more amps then designed for.

Its actually a great system

Hope this helps

John T