How to get a tach signal for N2O RPM window switch.

High everyone. I have a 2002 GT with COP. I have, and want to install, an rpm window switch for my nitrous system, and need a tach signal for it to work properly. The COP system uses separate coils, so tapping into one of them for the signal will not work. (Will only read 1 cylinder, giving 1/8 the actual RPM) Is there another way that I can get a proper tach signal???? I have heard of a special tach adaptor module that may do this, but I don't know what it is called, or where I might find it .

Any assistance is greatly appreciated.
Thanks,
Mike
 
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