RPM?Tach signal issues

[the tech]

After searching all of the 240sx/SR20 forums out there, I could not find the answer to this problem that I have. I recently picked up an 89 fastback with SR20det. Everything works well so far except for the tach. I have two DOHC clusters here and still can get no tach to work. After checking the yel/red wire, I come to find that it has been cut in several places. More research finds that it is not connected to anything in the engine compartment. I need to figure out where the wire is supposed to go and/or where the SR20 gets its tach signal from. I have checked the FSM and I can find nowhere where it tells where the ECU gets the RPM signal from.

All input would be helpful.

[Silvia007]

Here's a pinout.

[the tech]

Thanks for the help, but the pinout is not what I need.