Reading through this thread and what is and isn't working, I'd say it might be time to get the voltmeter out.
The OP says that a Nanocom can't connect to the engine ECU. It would be interesting to know whether it can connect to another ECU on the vehicle, say SLABS or the BCU. That would then rule out a problem with the diagnostics socket.
The OP has also said that he's had the engine ECU tested off the vehicle and it works OK. This would then point to something being amiss on the vehicle such as wiring, a fuse somewhere or maybe a faulty connection in a plug. An ECU fault could also be indicated by the odd indications on the dashboard.
Check or recheck the fuse F24 (10 amps) on the passenger compartment fuse board. If that's OK then a voltmeter check on pin 33 on the "B" plug (not the red plug) on the ECU with the ignition key in the II position. This supplies the working power to the ECU.