There's a lot of pages to the wiring diagrams, would take me ages to scan them all and they won't help you with a speedometer problem. I'm in the process of scanning the whole manual so I can host it on RapidShare, but it won't be finished for a few months.
If the car is left hand drive, the speedometer is operated by a traditional cable and doesn't involve any electronics.
If it's right hand drive, it's operated by an electronic pulse generator with 2 wires on top of the gearbox. They suffer from water ingress but can be dried out if you can get it open and back together again. I used to cut the metal securing band off, dry it out and reassemble it with large bore adhesive lined heat-shrink tube.
Dave.