Does a mag (-) wire give a signal?

General engine tech -- Drag Racing to Circle Track

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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.
Thinking is hard work.

sc2dave
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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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