Just wondering, I was getting ready to change out my gauge faces, and was curious which wire behind the tach is the RPM signal because I'm also going to install the Summit RPM switch.
Is it the white with green wire?

 

that's what i like to know also, i think i tried every single wire in the engine compartment and behind the dash for the signal wire and none of them worked. U can get a DIS TACH DRIVER from MSD ignition for cars with no distributor and muiltiple coil packs and that would the be the easiest way to go, it hooks up to each coil pack and a 12V supply and converts the information from the coil packs into a 12 V output signal used in a tach meter as a trigger signal.

 

Check out the FAQs in the turbo/supercharged forums. I think there is a thread in there on how to install the SAFCII which will show the ECU diagram which has the tach wire included.

-David-