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DonDittmar View Drop Down
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Joined: 15 Sep 2009
Location: MIllersburg, MI
Points: 2513 		Post Options Post Options   Thanks (0) Thanks(0)   Quote DonDittmar Quote  Post ReplyReply Direct Link To This Post Topic: IGN coil
    Posted: 30 May 2025 at 6:40pm
12 volt internally resisted coil, what’s a good spec for a an ohm reading? Got one testing at 3.5 ohms. Ole google is saying 1-1.5ohms, but that seems a little low
Experience is a fancy name for past mistakes. "Great moments are born from great opportunity"

1968 D15D,1962 D19D
Also 1965 Cub Loboy and 1958 JD 720 Diesel Pony Start
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steve(ill) View Drop Down
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Joined: 11 Sep 2009
Location: illinois
Points: 86258 		Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2025 at 6:44pm
should be 3 ohms... depending on the accuracy of your meter, your probably OK.

if it was 1.5, you would need the EXTERNAL resistor to go with it.

Measure the resistance on the OTHER SIDE of the coil and you should get  10- 20,000 type numbers.


Edited by steve(ill) - 30 May 2025 at 6:47pm
Like them all, but love the "B"s.
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WF owner View Drop Down
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Joined: 12 May 2013
Location: Bombay NY
Points: 4917 		Post Options Post Options   Thanks (0) Thanks(0)   Quote WF owner Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2025 at 6:55pm
I was always told that a 4 cylinder (12-volt system) should have a 3 ohm internally resisted coil.
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Les Kerf View Drop Down
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Joined: 08 May 2020
Location: Idaho
Points: 1115 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Les Kerf Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2025 at 8:29pm
12 Volts divided by 3.5 Ohms = 3.429 Amps through the points.

A more realistic 14 Volts divided by 3.5 Ohms = 4 Amps

12 Volts divided by 1.5 Ohms = 8 Amps.

You really don't want more than 4 Amps going through typical breaker points for longevity.


Edited by Les Kerf - 30 May 2025 at 8:30pm
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DonDittmar View Drop Down
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Joined: 15 Sep 2009
Location: MIllersburg, MI
Points: 2513 		Post Options Post Options   Thanks (1) Thanks(1)   Quote DonDittmar Quote  Post ReplyReply Direct Link To This Post Posted: 22 hours 23 minutes ago at 7:40am
Thanks all. This helps
Experience is a fancy name for past mistakes. "Great moments are born from great opportunity"

1968 D15D,1962 D19D
Also 1965 Cub Loboy and 1958 JD 720 Diesel Pony Start
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