We live and learn.
I said the speedo would be driven by a Hall Effect Sensor based on using the Revotec item that Dave W used.
It turns out it's not Hall Effect at all but a 3 wire inductive sensor.
It fooled me because I always thought Inductive sensors had 2 wires and Hall Effect had 3 wires.
Turns out that Inductive can have 2 or 3 wires.
Revotec confirmed it was Hall Effect but I think they were just happy to agree with me and stop me asking difficult questions.
Eventually I tracked it back to Schneider Electronics who burst my bubble by telling me it was something called a PNP Inductive Sensor.
Any way the nice people at VDO put me straight and told me how to wire the Speedo direct from the sensor without going via the ECU so thankfully back on track.
Just goes to prove that one should not believe everything one reads on TM
