Trouble wiring tach...

I have a '94 CX and I want to hook up the (-)Ignition wire up to my ECU (P05); instead of having to run the wires into my engine bay. Anyone know (or know where I can find out) what pinout I need to tap into? I'm under the impression that its' the A26 wire but I'm prob wrong. Thank you for any help.

doesnt the negative (-) go to the ground in one place or another anyway?

I think he's looking for the signal wire placement..? www.jdmfan.com has all the wiring pinouts, but the server never works. The negative can be hooked up anywhere on the metal chassis (under a bolt for example) and the positive to any 12V source.