It is installed!
Following the second diagram, your advices and Delicious instructions, I disconnected the box output (grey wire) from the passthrough and sent it to the ECU:
The reddish/black wire is the extension that goes all the way around the engine bay to the right grommet, then inside the cabin behing the dash:
Here is a very closeup of the ecu harness with the extension soldered and covered with heat shinking sleeve:
I used the Wayne CAT FLEX 147.DI, with the corected input voltages and here is a small log just to show how the ethanol content is measured (Excuse the poor ethanol ratio, aroung 54%, I had a geat load of unleaded 98 in the tank...):
https://datazap.me/u/ced67/wayne-cat...zoom=1371-6956
The correct reading is validated by the Delicious app that displayed the same % directly from the sensor.