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I went for a fairly long putt around town to celebrate the new exhaust bobbins that will actually keep the portside pipe from bouncing off an dragging on the pavement. Nearly home, I stopped at a red light and noticed that things had gotten very quiet. She wouldn't start. Added a trickle of fuel, turned the key, I'd hear the expected fuel pump run-then-stop. Still no start so I called a tow truck. At home, checked coil primary and got no continuity. Thinking I just wasn't getting on the contacts down inside the connector shell, I tried the secondaries and got about 10K ohms on each one. That's about what I was expecting, from my Google research. That confirmed that I was able to touch the contacts with my meter leads. Tried the primaries again with the same result. I expected to see 3-5 ohms but read infinity. Installed new NGK plugs. I'm now shopping for a coil. I assume that the coll for Harleys is much the same?

Any reason NOT to use a Harley p/n 31696-07A coil? USD 39.50 on Ebay.

If I had to replace a coil I sure would use the Harley coil. Easy to obtain and you don't have to import something.

I was mistaken about reaching the contacts properly on the primary resistance test. With the coil removed and using a light and narrow tester probes, I got 3 ohms on the primaries. Coil is fine. The problem turned out to be a failed timing belt.

Reply on “ Ign Coil Testing “

Hi all
I am not sure if I have a coil problem, the information here and on the internet is a little confusing.
In Ian’s alternative part-list he writes about the type ‘31655-99’

There are several Harley You-tubes about coil testing and most of them state that the primary should be around 3 Ohm.
And the secondary around 12k Ohm.
All single fire HD coils do have a three wire input for the coil.
From the three pins the middle one is the main Voltage and the two side pins are for triggering the front or the aft cylinder.
So measurements are taken from one of the side pins and the middle pin.

VA multi-meters are not correct when they have to measure 3 or less Ohm.
Because of the expected low Ohm on these pins, you can use two VA multi-meters. One as current meter and one parallel to the 12V source.
And calculate the Ohm – R = V/I -- out of the measured current and the measured Voltage.
I used a battery and a short push switch so I cannot damage/heat the coil.

I tested mine and the primary is around 0,75 Ohm and the secondary is 12kOhm.
So I thought mine is wrong and ordered a new one.
I tested the new one too and the primaries are again 0,75 Ohm and the secondary 12 kOhm.

I found a website with some HD coil info
http://xlforum.net/forums/showthread.php?t=1780092
There is stated
>> Single fire coil testing for carbed (ICM) rubsters, 2004-2006
Coil 31655-99 has three connectorized primary terminals (- + -), referenced 1 (rear) 2 (12 VDC) 3 (front) and twin coil towers.
Primary resistance is from + to -, both 2 to 1 and 2 to 3 at 0.5 to 0.7 ohms.
Secondary (high voltage) winding resistance is tested from coil tower to coil tower at 5,500 ohms to 7,500 ohms. <<

And
>> Single fire coil testing for Sportster Sport (1998-2003)
Coil 31646-99 has three connectorized primary terminals (- + -), referenced A (front) B (12 VDC) C (rear) and twin coil towers.
Primary resistance is from + to -, both B to A and B to C at 0.4 to 0.6 ohms. For the 1200S (dual plug heads), measure secondary resistance between both front coil towers and then between both rear coil towers at 11,700 to 12,700 ohms. <<

So this creates even more questions.
Q1 : Is this website correct?
Q2 : Do we really have a 31655-99 - it is printed on the new one, but not on the old one - because why then a secondary output of 12k instead of 7k Ohm?
Q3 : In this TM #578649 AncientMariner - I am an ancient Mariner too 😉 - speaks about 3Ohm but both the 31655-99 and the 31646-99 single coils do have 0,75 Ohm or even less.
What is the Ohm-reading we need on the Primary?
Q4 : What in case of a lower Ohm-reading
Q4 : Where to find the correct specs?

Thanks

PS TM Posting editor seems to be really slow at the moment.