tach signal

With what, MSD ignition? What is the part no. of this adapter? Link?

You mean an Equus tach? what model? Link?

One set of destructions I found for Equus indicated they could also be triggered inductively off the coil wire / plug wire

https://www.google.com/url?sa=t&rct...M12pMFTDwEQWN89YQ&sig2=-CgglfH9W34ozfNB2ud0IQ