Ohms in a stock coil
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Fleet Owner
Joined: Dec 2000
Posts: 25,310
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From: Central PA
Ohms in a stock coil
Can anyone tell me something about ohms in a coil? I bought a new coil at a parts store 2 weeks ago. Then I decided to buy an electronic ignition. That company says your coil must have 1.5 ohms of primary resistance. Obviously I don't want to buy another coil. Of course the electronic ignition company wants to sell their coils. I called the parts store to ask them what the ohms was on the coil. They looked in their books but could not find it.
This coil is for a 1970 F350 with a 360. On the coil are printed these words: "12V use with primary resistance wire or external resistor 067." I called the local auto electric shop that rebuilt my starter and told me my old coil was bad. They can not tell what the primary resistance is on a coil, only if it is good or bad. He recommended looking in a 1970 truck shop manual.
Can anyone help me? A Pertronix Flame Thrower coil costs $31.95. I don't know if I can take my other coil back to the parts store. It has been on the truck but driven only 4 miles......
Thanks and Happy New Year!
This coil is for a 1970 F350 with a 360. On the coil are printed these words: "12V use with primary resistance wire or external resistor 067." I called the local auto electric shop that rebuilt my starter and told me my old coil was bad. They can not tell what the primary resistance is on a coil, only if it is good or bad. He recommended looking in a 1970 truck shop manual.
Can anyone help me? A Pertronix Flame Thrower coil costs $31.95. I don't know if I can take my other coil back to the parts store. It has been on the truck but driven only 4 miles......
Thanks and Happy New Year!
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
That coil should have next to no resistance. It's designed for an exrernal resistor.
To measure the coil's resistance is fairly simple. Get an ohmmeter touch one of the probes to the coil tower and the other probe to the + termnal.
To measure the coil's resistance is fairly simple. Get an ohmmeter touch one of the probes to the coil tower and the other probe to the + termnal.
Posting Guru
Joined: Mar 2006
Posts: 1,182
Likes: 1
you won't be able to return a used ignition coil.
i think the stock coils are 3 ohms.
to measure- just put your voltmeter leads across the + and - terminals.
what electronic ignition have you purchased?
i'm sure someone will correct me if i'm talking out of my rear here, but-
i imagine that the the directions from the ignition mean your coil must have *at least* 1.5 ohms of primary resistance.
i think the stock coils are 3 ohms.
to measure- just put your voltmeter leads across the + and - terminals.
what electronic ignition have you purchased?
i'm sure someone will correct me if i'm talking out of my rear here, but-
i imagine that the the directions from the ignition mean your coil must have *at least* 1.5 ohms of primary resistance.
Thread Starter
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Fleet Owner
Joined: Dec 2000
Posts: 25,310
Likes: 5,348
From: Central PA
you won't be able to return a used ignition coil.
i think the stock coils are 3 ohms.
to measure- just put your voltmeter leads across the + and - terminals.
what electronic ignition have you purchased?
i'm sure someone will correct me if i'm talking out of my rear here, but-
i imagine that the the directions from the ignition mean your coil must have *at least* 1.5 ohms of primary resistance.
i think the stock coils are 3 ohms.
to measure- just put your voltmeter leads across the + and - terminals.
what electronic ignition have you purchased?
i'm sure someone will correct me if i'm talking out of my rear here, but-
i imagine that the the directions from the ignition mean your coil must have *at least* 1.5 ohms of primary resistance.
What do you think?
Posting Guru
Joined: Mar 2006
Posts: 1,182
Likes: 1
i looked up the Hot Spark (hadn't heard of it before, but looks like the Pertronix).
it says "works with stock coil", and also as you noted, "6- and 8-cylinder distributors require a coil with 1.5 or more Ohms primary resistance"
you'll be fine with your stock coil.
it says "works with stock coil", and also as you noted, "6- and 8-cylinder distributors require a coil with 1.5 or more Ohms primary resistance"
you'll be fine with your stock coil.
Thread Starter
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Fleet Owner
Joined: Dec 2000
Posts: 25,310
Likes: 5,348
From: Central PA
i looked up the Hot Spark (hadn't heard of it before, but looks like the Pertronix).
it says "works with stock coil", and also as you noted, "6- and 8-cylinder distributors require a coil with 1.5 or more Ohms primary resistance"
you'll be fine with your stock coil.
it says "works with stock coil", and also as you noted, "6- and 8-cylinder distributors require a coil with 1.5 or more Ohms primary resistance"
you'll be fine with your stock coil.
thanks!
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
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Posting Guru
Joined: Mar 2006
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that would measure secondary resistance- but the OP is looking for primary resistance. secondary resistance would be extremely high- more than 10,000 ohms.
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Posting Guru
Joined: May 2001
Posts: 1,395
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From: Cupertino
I checked the 1967 Ford Truck Manual, Part 9-7, ignition system specifications.
Coil Primary Resistance 1.40- 1.54 ohms.
Coil Secondary Resistance 7600-8800 ohms.
Both at room temperature.
Being a transformer, the isolation resistance between primary and secondary should be infinite.
Semper Fi, Happy New Year
Coil Primary Resistance 1.40- 1.54 ohms.
Coil Secondary Resistance 7600-8800 ohms.
Both at room temperature.
Being a transformer, the isolation resistance between primary and secondary should be infinite.
Semper Fi, Happy New Year
Thread Starter
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Fleet Owner
Joined: Dec 2000
Posts: 25,310
Likes: 5,348
From: Central PA
Thanks, that is what I was looking for, something out of the shop manual from Ford. With that and the fact that Hot Spark says you can use the stock coil (if it is 1.5 ohms) I feel safe using it. I am stuck with it since I installed it on the truck. It is only about 2 weeks old and only driven 4 miles.
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