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Motorcycle Repair/1996 Honda Shadow 600 VLX


QUESTION: Hi Wayne ,
My friends 600 Shadow was only running on the rear cylinder . I can tell by the sound and only the rear exhaust pipe is getting hot . I removed the gas tank and found a mouse nest on the front ignition coil . Mice had chewed through the coil wires . I thought this would be an easy fix , just repair the chewed wires . So with the wires repaired ,it still doesn't fire on the front cyl . I swapped the coils and I still only get spark at the rear cyl . so both coils are good . A test light shows power at the coils with the key turned on .I checked the service manual on how to do further testing but it says that you have to use a 10M ohm DCV multimeter .I don't know if my multimeter is 10M ohms . Can you shed some light on how to proceed .

ANSWER: Hi Rick,

If the coils are both good then you have to check the other
parts of the ignition system.

I would pull the left side cover and tool box ect and get the ICM
or ignition control module out and check the wires on that.
Some good electronic spray cleaner might help clean the connector.

Check the connector and pins, clean it and reconnect it.

The ignition pulse coil may be poorly connected or maybe more
mouse damage.
Check the white/blue to blue pulse connector wires for about 0.7 volts
when cranking.

If you want a working reading check the other pulse connector for the
rear cylinder which is white/yellow to yellow. You know that one is working.

These connections can be made either near the front left wiring harness or on the ICM unit.

Both pulse coils should have similar readings.

It might be a bad connection or a faulty pulse coil.
The pulse is sent to the ICM to tell it to fire.

Also keep battery voltage up when testing.

Hopefully I got the wire colors correct for you.

Wayne S

---------- FOLLOW-UP ----------

QUESTION: Hi Wayne ,
Thanks for your quick response yesterday .
I checked the connections at the ICM and everything is good . It looks like Honda or some one coated the pins with dielectric grease .
The colors of the wires at the 4 pin connector of the ICM  are not as you described .
The wires coming out of the ICM are
On the harness side it is
The wires at the front ignition coils are blue/white and blue
The wires at the rear ignition coils are  white/yellow and yellow

So am I to check the voltage at the coils or at the ICM ?
Do I leave the coils or ICM connected when checking ?
Thanks for your patience .


I can't find any 600 Shadow with those ICM colors.
I will see what I can find and get back to you asap.

Are you sure you were looking at the ICM and not
some other electronic component?

The ICM has 10 wires G, Y/Bkue, Black, Blue/Y, Lg/R
G/W, Y, W/Y, Blue, W/Blue.

The voltage tests I wanted you to try were on the electronic
pulse coils that are inside the engine.
The colors of the wires should be as I listed before.

These are not the ignition coils these are trigger coils
to make the ICM fire the main ignition coils.

Just find the wires that come out of the engine case
and follow them then disconnect them and do the
voltage test while cranking.

There are two pulse sensors or coils, one for each cylinder.
The rear one must be working so it should have a reading.
See if the other one is reading similar.

Let me know if you need or have more info.

Wayne S.


---------- FOLLOW-UP ----------

QUESTION: Hi Wayne  ,
So it seems I was confusing the rectifier with the ICM .
I found the ICM behind the rectifier and checked the voltage readings .
Still kind of confused as the readings for both were .03 volts , not .7 volts, but since they are both the same and the rear cyl. does fire , I'm going to assume the ICM is bad . The manual does say that the ICM can be damaged by bad connections , like the mouse severed wires at the front coil . Would you agree with this diagnosis ?
Thanks again , Rick

Hi Rick,

Can you swap the pulse coil connections to see if the ICM will
fire on either pulser?

The bike won't run but you should still get a spark when you swap
the pulsers if the problem is one of the pulse coils.

If the front still won't fire after you swap the pulse connections
then I would assume the ICM is damaged.

You may have to rig some jumpers unless the pulse wires
can just be swapped and connected again.

Rear pulser is white/yellow to yellow.
Front pulser is white/blue to blue

The rear is firing so connect the white/yellow to the
white/blue in the harness and the yellow to the blue
in the harness to see if the front plugs will fire with the
known good pulser.

If the front still has no spark then look toward the ICM.

Wayne S

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Wayne S.


Licensed Motorcycle Mechanic, Knowledge of motorcycles from 1960 up, Japanese, British and most other brand motorcycle repairs.


Worked for Yamaha, Honda, Suzuki, Kawasaki British: Triumph, Norton, BSA Other: Most Scooters and Mo-Peds

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