Speedometer + Spoiler + OBC inoperable

[hexagone]

Have been trying to diagnose a fault:

My speedometer does not work, and as a result the spoiler light is on, and the OBC does not read speed either. '97 Tiptronic 993.


* ABS works. All Speed sensors ohm at ~1700. No ABS light.

* Driving the car, the ABS engages fine.

* Speedo still not working, spoiler light turned on. Can't imagine the ABS ECU is at fault either because ABS works and no light is on.

*The OBC does not receive a speed signal either. What does that indicate?



The problem is also identical to the one below, but none of his fixes (short of replacing the ABS ECU) have helped:

Speedometer, OBC and Spoiler weird Problem