6v vs 12v coil

Minn-Tex Lee

Minn-Tex Lee

Senior Member
Getting ready to change out my defective coil on my 12v system I discovered an interesting fact (which most of you probablly know).
There is NO difference in the electrical properties of the two coils.
You pay $5.00 for a printed lable on the can that says "To be user with a dropping resister 12 V". There are two different part numbers in "Obsolete" catelog for the two different parts.
Here all along I thought the 12 V coil was somehow different.
Oh well - live and learn.
Lee
 
I don't think that is 100% correct in all cases.

If I remember right, a reading across the posts of a 12 volt coil should be about 3 ohms. A 6 volt coil is about half of that, while not exact it is close enough that you can tell 6 from 12 volt.
 
Close reading of Echlin and Standard catalogs will identify some...most of the coils, though, are sold as replacement for particular cars and you need to know what that car used.
I have an olde NAPA catalog here, their IC 672 comes with bracket and is labeled as non-resistor type 12V.
It's your basic cylindrical type that would mount like a Model A coil. Standard UC 15 or UC 15X (the higher grade) seem about the same.
If using a resistance one...get it for something specific, like '65 Mustang, and buy the resistor that goes with it...there are numerous different resistance values out there.
 
Although Snyders does not sell 12v coils they can give you a part number and you can get one from Auto Zone or other auto parts store. I bought mine at auto zone . Resistor intergal with coil.
 
Model A Coil primary resistance ( low tension side) is 1.2-1.4 ohms for straight poll coils. Slant polls can be slightly higher. Slant polls are the hotter of the two coils. I have tested hundreds on my Ford heyer stroboscope. BTW Mike is correct on half the resistance.
Larry S
 
6v coils use no resistor. 12v coils can be either way, internal or external resistor and should be marked as such. But, of course, not all are. Most auto manufacturers have used both style coils depending on the application. That said, I can't remember GM using an external resister coil. All you have to do is measure the voltage coming out of the coil, once warm the one with the resistor will drop the 12volts to 6-8v. Also most oil filled coils don't like to be mounted upside down.
 
Yep. Any auto parts store can get one if it doesn't already have one in stock. They will probably ask you the ding dong question of " What are you working on ? " tell them it's a 72' chevy. It used the internal resistor on my truck.
 
You can use an original coil on 12 volts but you will have to use an external resister . Coils that are rated at 3.0 ohm have an internal resister and will run 12 volt on the model A as is. Another concern is what the coil is filled with. Original model A coils were tar filled. More recent coils are either oil or epoxy filled. Model A coils were mounted with the wires connected pointing down. More recent oil filled coils are mounted with the tower pointing up. When oil filled coils are mounted with the tower pointing down the oil doesn't completely cover the internal coil of wire, the coil over heats and doesn't last as long. The oil can sometimes leak out if the coil is mounted as model A coils originally were mounted. I use an epoxy filled 3.0 ohm ,flame thrower coil from Pertronix on my 12 volt model A roadster. This is a performance coil that is twice as powerful as the original slant pole model A coil. The epoxy filled flame thrower coil can be mounted just like the model A coil with the wire connections at the bottom.The original slant pole coil was rated at around 20.000 volts. The Flamethrower coil is rated at 40.000 volts and gives electronic like performance for about forty semething dollars. I get instant starts, the plugs run clean and you can feel the better performance. I got mine from Eastwood.
 
Thanks to Purdy Swoft I run Pertronix "Flame Thrower" coils on both my "A's". A 3-ohm coil on the 12 volt '29 and a 1.5-ohm coil on the 6 volt '31.
They do make a difference.;)

Bob-A:D
 
Every coil Snyders sells is 12v. If you peel the sticker off it says 12v right underneath. Every single one I've got from them has it. Have your local autoparts store get the coil for a 57 Chevy, they have an external resistor and everyone has a 57 Chevy in their system.
 
Minn-Tex Lee said:
Does anyone know where I can find the one with the built in resistor Lee
Click to expand...

NAPA coil IC-14 is one source of what you want. It is an internal resistor coil for use on 12 volts. I am sure there are others. My NAPA keeps them in stock.
 
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The GM cars after the mid-'50's or so had resistors...not a visible separate part, but the feed wire to coil from switch was resistance wire, with both the actual wire and the insulation very odd looking stuff. There was also a second wire feeding straight 12 when starter was engaged.
 
Thanks for all the replys. I got the NAPA - IC14 since I have a NAPA store close by.
It looks like a 12 volt coil that says "external resisror required " is really a 6 volt coil.
Lee
 
I never really knew all this....but it sounds like every coil is a 6 volt coil. You either feed it 6 volts from the battery, or you use a resistor to get the 12 volts down to 6 before the coil....whether its external or internal is up to the MFR.
Thanks for the info guys.:)
 
Delco 6-volt internal GM # 1115380
Delco 12-volt internal GM # 1115238
Delco 12-volt external GM# 1115202
Ford 6-volt external Ford # 8BA-12029
Ford 12-volt external Ford #D0RY-12029A
Ford "blue top" internal for electronic ignition Ford # D5AZ-12029A
Chrysler 6-volt firewall-mounted Chrysler # 862576
Chrysler 6-volt internal Chrysler #1300667
Chrysler 12-volt external Chrysler #2495531
Chrysler "tan top" external for electronic ignition Chrysler # 4176009

Here is a list that should cover probably 99% of all applications.
 
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