I have a series 4 RX7 N/A does anyone know what color the tach signal wire is; running to the ecu @ driver's side kick?

 

The yellow/blue wire running to the back of the cluster is for the tach.

You can also use the diagnostic bullet connectors on either of the coils to get a tach signal. Again, you want the yellow/blue wire.

The yellow/blue wire shows up in a bunch of places inside the car. The ECU and power steering computer also tap into it.

 

It's obviously been a while but anyone still looking for this info and you don't wanna splice wires at the ecu or diagnostic port. You could put an eye hook on the wire and attach it to the negative post of your leading coil. Or trailing coil but leading has the best results.