Did you figure this out yet? Cause i did just now:) bought a third omega. A 97 2,0 estate. One owner car has done just 60.000km. Had a tid fitted but it was completely gone. Only about 5 pixels still working. Figured out i would buy a grey plug mid since i needed a display anyway and dont want to be annoyed with pixel failures. Ran into the same problem you did. Radio info, and check control worked fine, but fuel computer functions was dead. Started crosschecking the pin list in this theead (which i followed) with Haynes. Turns out whoever wrote this list mixed up the wire colours on fuel sender and speed sensor. Pin 12 and pin 26 on the grey plug needs to be switched around. 12 should be blue/red and 26 should be blue/black. Everything working great now.
Also job was much easier than it seems in the guide. This poverty spec 97 with a tid had ALL the wiring in place already. Yellow plug obviously in the tid, but the black plug with the rest og the wires was taped up just behind it. And behind the fuse box the multipin connector for the bulb control was present. Also wiring for the new stalk was present in the steering coloumn. Only needed the mid with plug, new stalk, bulb control unit and the various sensors in the engine bay. Wiring present for them to:) Happy days!