SR Tach Wiring Problem

[shaggy240sx]

So apparently I am a dumbass so I am hoping someone here can help. I tried searching both here and google and have come up with nothing (again...could just be that I am a dumbass).

I have a 90 240sx with a Redtop SR20det. I know that the 89-90 tach will not work because of something with the signal. I could not seem to track down a 91+ gauge cluster so I decided to pick up an aftermarket tach. I hooked up the power and the ground and then spliced the signal cable into the yellow/red wire on the ECU that is supposed to be the Tach signal and got nothing. Then tried to splice it to the "signal" wire on the top of one of the coil packs and still got nothing. When the power is hooked up the gauge goes to 0, so I am fairly certain the ground and power are good, it just doesn't seem to be getting signal.

Obviously I am doing something wrong (or maybe the tach just isn’t compatible...but it is brand new so I wouldn't suspect that), but I can't seem to figure out what. Any help would be greatly appreciated.