IH 454 coil issue

This tractor is a 12 volt and always has been.

When I purchased the tractor it had a 6 volt coil on it. It looked like it was the original coil that came with the tractor.

Why did they use a 6 volt coil on a 12 volt tractor?

Is it ok for me to use a 12 volt coil instead?

Would I need to use a resistor with either coil?

Thanks for your advice.

Napa sells a 12 volt coil with a builtin resistor
p/n ECHICR13 for about $14.00. Hal

There is no such thing as a "6 volt coil" or "12 volt coil" in regard to the system voltage, so you need to be more specific. A coil made to run full time on 6-8 volts is the most common for 12 volt systems with breaker-point ignition. The same is often use on 6 volt systems also.

Ingition systems are designed for specific voltages, and the coils in those systems can have many different values.

Just make sure you have no upstream (toward key switch) resistor in the system when using a true 12v coil. JimN

Echlin ICR-13 at NAPA is a 1.8 ohm resistor, not a coil.

You need to know exactly what coil you bought. The 6 volt or 12 volt designation doesn't mean anything by itself. Many tractor companies (and cars and trucks) have exactly the same coils on 6 and 12 volt systems. Especially IH and Deere.

Since you bought a new coil, you need to know either the specs on it, or what the company that made the coil says how it's supposed to be used.

Many over-the-counter coils are called "12 volt" are really meant for a 6 volt system with no resistor, or a 12 volt system with an added 1.8 to 2.2 ohm resistor.

What coil did you buy?

I will take your questions one at a time:

QUESTION: Why did they use a 6 volt coil on a 12 volt tractor?

ANSWER: One possible advantage is to improve starting at cold temperatures when battery voltage can be drastically reduced while cranking. Its quite common to use a 6 volt coil on a 12 volt tractor and add an external series voltage dropping (12 to 6) Ballast Resistor after the switch and before and ahead of the coil, that way the 6 volt coil operates at its designed intended 6 volts to avoid overheating and over current, plus the points only have to switch around 4 amps so they dont burn prematurely... HOWEVER during cranking when battery voltage drops which can reduce spark energy, THE BALLAST IS (or can be) BY PASSED resulting in a hotter starting spark that would occur if it were a 12 volt coil with no ballast capable of being by passed during cranking. They run on 6 volts but start on 12 (as reduced by cranking amps)


QUESTION Is it ok for me to use a 12 volt coil instead?

ANSWER YES INDEED you can use a full true (some call internally ballasted) 12 volt coil NO BALLAST REQUIRED. You would loose the benefit available if it was equipped with a 6 volt coil and external ballast and had the start by pass system, however.

QUESTION: Would I need to use a resistor with either coil?

ANSWER: Yes you need an external series voltage dropping (12 to 6) ballast resistor if its a 12 volt tractor and you use a 6 volt coil WELL DUH..
HOWEVER YOU DO NOT need an external ballast resistor if its a 12 volt tractor AND YOU USE A FULL TRUE 12 VOTL COIL. NOTE some of the Older Fords still require an external series ballast

THE DIFFERENCE IN 6 AND 12 VOLT COILS

a) A typical 6 volt coil has around 1.25 to 1.75 or so ohms LV primary winding resistance and it and the points draw and switch around 4 amps on a 6 volt system... b) A typical full true 12 volt (some call internally ballasted) coil has around twice that (2.5 to 3.5) ohms primary and draws around 4 amps on a 12 volt system (as does a 6 volt coil + ballast).

Some coils are labeled "12 volts" and they are indeed designed to operate at 12 volts WELL DUH.......Some coils are labeled "6 volts" and they are desigend for 6 volT use WELL DUH....Some coils are labeled "12 volts NOT for use with external ballast resistor" that means just what it says......Some coils are labeled "12 volts requires (or for use with) external ballast resistor" again it means what it says.

I hope this explains all the 6 volt versus 12 volt coil and external ballast resistor thing, if I missed anything I'm sure the other fine gents can add to this......

God Bless n Merry Christmas

John T

Problem is, an awful lot is not "typical." Coils can vary wildly, regardless of that they are called (by system voltage). Checking ohms is not a accurate indicator of what a coil was marketed as.

NAPA 12 volt coil- IC-27 Echlin 2.2 ohms primary, 6.38K ohms secondary

John Deere 6 volt coil- 2.6 ohms prim, 7.12K secondary as used on 430 with 6 volt system, 1010 with 12 volt system, etc.

NAPA 12 volt coil IC-12 Echlin 2.1 ohms primary, 8.9K ohms secondary

Mallory 29217 12 volt breaker-point coil, primary 1.4 ohms, secondary 9.8K ohms

Accel 12 coil for points, 1.4 ohms primary resistance, 9.2 k ohms secondary resistance

IH tractor ignition coil - 6 and 12 volt
396546R93---Ignition coil for 6 volt systems, with or without external resistance. For 12
volt systems with external resistance. Replaces IH coils: 353874R91, 368839R91, 395330R91 & R92. DELCO COILS: 1115084, 1115098, 1115407.

I sure agree, there are indeed many variations, many are "typical" of the garden variety for older tractors I used (many of those 6 volt are around 1.5 ohms, many of those 12 volt are around 3 ohms) for my examples, while some others such as your research shows are NOT, but most old tractors Ive seen didnt use Mallory or Accell coils. We just cant say sittin here what the posters may have and unfortunately they cant usually tell us either grrrrrrrrrrrr........

Good info on certain particular models (though some you cite like Mallory or Accel arent so much for older tractors as I stated above), now if we only had alllllll the coils used on allllllll tractors and then the posters had the part numbers we could give them better answers, Oh well we do our best with the limited info we usually have to work with lol.

Best Wishes n God Bless

John T

The later model IH gasoline tractors used a resistance wire between the switch and the solenoid instead of a separate ignition resistor. Use of a 12 volt coil designed to be used without an external resistor is going to result in low voltage at the coil as soon as the solenoid disengages.

I should've known that since I have both numbers written down. Thanks, Hal

I should've known that since I have both numbers written down. Thanks, Hal

The Accel and Mallory units I gave specs for are the "retro" versions they sell for older cars and tractors with breaker-point ignition.

The Deere 6 volt/12 volt coil is a bit unusual with the high ohms on the primary. Higher then many "12 volt" coils. Was trouble free on old two-cylinder tractors with 6 volt systems. But, when used on the "new" 1010s and 2010s we had a lot of trouble. Mostly with points burning out fast. Deere had several updates and also offered three different ignition systems. The coil I gave specs for is the Delco system. Same 1010/2010 also came with a Wico or Prestolite, and both of them had their own coils.

My main point here was and is, you can't just stick an ohm meter on a coil and decide was it was marketed as (6 volt or 12 volt system use).

It's fresh in my mind because I bought a bunch of resistors last week at my friends NAPA store. I was also checking current prices of NAPA Echlin coils and they are now around $40 each.