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when the car is running the coil wire should be in A/C voltage, not D/C. I think you have the wrong coil wire going in to the tach. Thats the input to tell it how fast the engine is spinning. It creates an A/C voltage that goes up with RPM.
 

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You want to ground the black lead and use the red lead to test whichever wire you think is your tach signal wire coming off the coil. Like I said before its A/C so make sure you set the DMM to A/C voltage. The right wire will go up in voltage with RPM's. It was dk. green/yellow on the stock coil, but I remember you saying you had an aftermarket.
 

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Discussion Starter #5
well how bout this? can i just cut the wire that runs for the stock tach? and use it on the aftermarket?
 
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