Does a mag (-) wire give a signal?

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JohnP
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Re: Does a mag (-) wire give a signal?

Post by JohnP » Fri Oct 20, 2017 2:21 pm

sc2dave wrote:
Sun Oct 08, 2017 11:46 pm
Trying to see if my Neg mag. pickup wire is giving a signal to the MSD box for it to signal. I have tried grounding the white wire and the box makes the coil spark, but I want to find out if the mag is indeed sending some signal. Can I check this with a multimeter?
Let's start over. :)

What you were calling mag pickup wires are really the outputs of the stock ignition. These outputs are open collector transistors used to ground the coils during dwell, then unground them to make the spark.

A good way to test them is to use an old fashioned 12v test light. Connect the alligator clip of the test light to 12v, then probe the "Neg mag. pickup wire". The light should blink as you crank the engine. The light will turn on during dwell, then turn off when your stock ignition triggers the MSD.
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Re: Does a mag (-) wire give a signal?

Post by sc2dave » Sat Nov 25, 2017 11:26 pm

JohnP wrote:
Fri Oct 20, 2017 2:21 pm


Let's start over. :)

What you were calling mag pickup wires are really the outputs of the stock ignition. These outputs are open collector transistors used to ground the coils during dwell, then unground them to make the spark.

A good way to test them is to use an old fashioned 12v test light. Connect the alligator clip of the test light to 12v, then probe the "Neg mag. pickup wire". The light should blink as you crank the engine. The light will turn on during dwell, then turn off when your stock ignition triggers the MSD.
Ok. I'll try this tomorrow. Sometimes the bike don't even want to turn on. if I ground one of the wires so that it makes the coil spark, it'll start after, when I crank it

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Re: Does a mag (-) wire give a signal?

Post by sc2dave » Tue Dec 19, 2017 2:11 pm

JohnP wrote:
Fri Oct 20, 2017 2:21 pm
sc2dave wrote:
Sun Oct 08, 2017 11:46 pm
Trying to see if my Neg mag. pickup wire is giving a signal to the MSD box for it to signal. I have tried grounding the white wire and the box makes the coil spark, but I want to find out if the mag is indeed sending some signal. Can I check this with a multimeter?
Let's start over. :)


A good way to test them is to use an old fashioned 12v test light. Connect the alligator clip of the test light to 12v, then probe the "Neg mag. pickup wire". The light should blink as you crank the engine. The light will turn on during dwell, then turn off when your stock ignition triggers the MSD.
Now, this "Neg mag. pickup wire" would be the neg wire from the stock bike wiring, and not the wiring coming from the msd box?

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Re: Does a mag (-) wire give a signal?

Post by JohnP » Tue Dec 19, 2017 2:20 pm

Yes, the stock wire that would normally connect to the coil negative.

That wire should be able to blink a test light. Use the kind that has a light bulb in it.

Connect one lead to 12v, the other to the stock coil negative wire. The light should turn on in dwell, turn off to make the spark.
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Re: Does a mag (-) wire give a signal?

Post by sc2dave » Mon Dec 25, 2017 8:06 pm

Ok. I hooked up a test light to one of the neg wires. The test light was lit up before I cranked it. Once I cranked it, the light went dimmer. I don't believe that it turned off and on when I cranked it.

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Re: Does a mag (-) wire give a signal?

Post by joe 90 » Mon Dec 25, 2017 8:15 pm

An oscilloscope is the right tool for the job, test lights are pretty useless at most things.

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Re: Does a mag (-) wire give a signal?

Post by JohnP » Mon Dec 25, 2017 9:44 pm

Joe, it's the wire that goes to the coil neg.

It looks like your stock ignition module is bad. The light should turn on and off each time that cylinder comes up.
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Re: Does a mag (-) wire give a signal?

Post by sc2dave » Mon Dec 25, 2017 9:59 pm

JohnP wrote:
Mon Dec 25, 2017 9:44 pm
Joe, it's the wire that goes to the coil neg.

It looks like your stock ignition module is bad. The light should turn on and off each time that cylinder comes up.
The bike is a 4 cyl, waste spark setup. It has a single pickup. Can I wire the MSD box straight to the pickup coil?

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Re: Does a mag (-) wire give a signal?

Post by JohnP » Mon Dec 25, 2017 10:18 pm

According to the MSD instructions, it will not trigger directly from a magnetic pickup. It needs to be triggered from an ignition module or points.
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Re: Does a mag (-) wire give a signal?

Post by sc2dave » Mon Dec 25, 2017 10:31 pm

I read the instructions and this is the only part that I read about triggering; "The MSD MC-2 Ignition can be used on 2 or 4-cylinder engines using two coils. The MC-2
will operate with conventional points or from the amplifier of an electronic breakerless
system. Capacitive discharge units cannot trigger the MSD" The stock ignition is not C.D.

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Re: Does a mag (-) wire give a signal?

Post by JohnP » Tue Dec 26, 2017 6:36 am

Yes, the MSD will trigger from points or from the OUTPUT from an electronic ignition, but it cannot trigger from the input wires that trigger your electronic ignition.

The test light shows your ignition module is bad. Replace it then verify the engine runs normally on stock ignition before installing the MSD.
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Re: Does a mag (-) wire give a signal?

Post by sc2dave » Tue Dec 26, 2017 10:41 pm

Do you think that it's possible to install an HEI module, with the right amount of pins, to replace this ignitor box? I know i'd have to make connectors for it

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Re: Does a mag (-) wire give a signal?

Post by JohnP » Wed Dec 27, 2017 1:22 am

Don't try to use the four pin module. It won't work unless it's connected to an ignition coil.

Mega Squirt has information about GM modules:

http://www.megamanual.com/ms2/GM_7pinHEI.htm
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Re: Does a mag (-) wire give a signal?

Post by sc2dave » Wed Dec 27, 2017 7:59 pm

Will this work? http://www.geocities.ws/loudgpz/GPZgmHEImod.html Where would I connect the MSD box to?

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