inline resistor from coil

rewiring my farmall 300 is it necessary to put an inline resistor on positive side of the coil if u have a 12 volt coil already . thanks

no

If it is a true 12 volt coil no resister needed but there are coil that are made that say 12 volts but need a resister and then there are one made that do not need a resister so you have to know what you have. Many will say on them 12 volt resister needed and others will say 12 volt no external resister needed

thatswhat i said

1) I believe (NO Warranty) "some" Farmalls used a 6 volt coil on a 12 volt tractor but the ballast resistance was in the form of a resistive wire link NOT a discrete bathtub style looking ballast, so if that's what you have and its still wired that way you need a 6 volt coil...

2) In GENERAL if its a 12 volt tractor and there's NO ballast device, you use a full 12 volt rated coil no ballast required

ORRRRRRRRRRRRRR a 6 volt coil PLUS an external series voltage dropping (12 to 6) ballast resistor

3) A coil labeled "12 Volts" or "12 volts NOT for use with ballast" is a full 12 volt rated coil

4) HOWEVER a coil labeled "12 volts for use with ballast" is in reality just what it says and is more like a 6 volt coil

5) Many (not all) 6 volt coils have a LV primary winding resistance of 1.2 to under 2 ohms while many (not all) 12 volt coils have a LV primary resistance of around 2.5 to 3.5 or so ohms

NOTE since this is an old tractor forum I'm talkin typical old "farm" tractor coils NOT many of the wide variety of auto or truck coils as some American made cars n trucks used 6 volt coils and other 12 volt coils with different ranges of ballast resistances to match the different coil resistances etc etc etc ................

I have found full 12 volt or 6 volt coils at NAPA and they cost less then if bought at Deere or IHC etc

John T

All you said was NO which does not tell the guy much if any thing.
You know good and well there are coil that are labeled as 12 volt coil but need a ballast resister. You also know there are coil labeled as 12 volt that do not need a ballast resister and depending on which one you have it can cause many odd problems if not wired the correct way