Just to clarify for you guys, the speedo gets it's signal directly from the speed sensor. These wires (y/l, y/b) connect at the passenger side relay box and wind around to the cluster by going in front of the radiator and up through the SMJ. The yellow/green is the speedo OUTPUT, which tells the ECU how fast you're going.

If your odo doesn't work, make sure the small white connector on the lower, back area of the cluster is connected firmly. The speedo's needle and the odo servo are driven from the same control board.

It's not uncommon for the wire to be missing on a used harness. Removing it effectively performs a speed limiter removal (and also makes your car more prone to stalling at lights). Find a pinout for the ECU and locate this pin position. If theres nothing there, you might be able to steal a pin from an unused function or another harness.