RPM Signal Wire?

[motorhead]

I am installing my HKS Type-1 Turbo Timer and I need to know:

Which wire is used as the RPM signal.

To Tach?
To ECM?
From ECM?

Thanks,

 

[motorhead]

TTT

 

[Black Car]

Behind the alternator on the 86-87 you will find two white wires going into a green connector. This is what you want to use for rpm/tach signal.

Gary