Mine has a small box on the bulkhead where the two speedo cables join. It also has connections to the ecu. Bit of a fiddle to remove and open (its not supposed to be opened). Inside theres an inductive rotor that obviously sends info about the cars speed to the ecu.
I had some problems with mine (it was squeaking loudly) so I disconnected it and the idle speed increased.
As they are made from unobtanium I decided to carefully open it up and clean it out. It was full of white powdery corrosion and once cleaned and reassembled has worked perfectly and the squeak has gone.
