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Which Wire Coming From the Coils is Negative?

NatetheNoob

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I’m hooking to a digital tachometer and need to tap in. My instinct tells me it’s the black and white connecting to the kill switch.
 
Only if the unit can read the primary side (+), most tachs read the negative side, which is split in two coils.
 
Only if the unit can read the primary side (+), most tachs read the negative side, which is split in two coils.

Thanks. This is the only of three wires comingFrom the coils that connects to both, and also the kill switch. Fair to say it’s the negative, therefore the appropriate wire to splice into for my tachometer.
 
Nope, it's the positive. Negatives (blue and yellow) are split and go into the two spark units or ignitors. I guarantee it. You can't join the two together it will short out both the coils, reading only one is a two cylinder engine not four. Beginning to see the problem yet?
 
Nope, it's the positive. Negatives (blue and yellow) are split and go into the two spark units or ignitors. I guarantee it. You can't join the two together it will short out both the coils, reading only one is a two cylinder engine not four. Beginning to see the problem yet?
So the yellow and blue wires go to the negetive posts on the spark units and the others go on to the positive post, (1982 cb750c)
 
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