Ok, I see a couple of you have a problem here, so to clarify.
If on the 1988 model you have the rev counter that only covers 2/3 of a revolution and the 4 5 and 6 are in a straight line then it's the early type and ddriven by a speedo cable. I'm desparatley trying to picture it in my head and I've been driving one all day. The rev counter as said works from a thin wire on the back of the alternator.
If you have the 1988 onwards model, the Hot-Wire EFi in fact then you may will have the electronic speedo which is layed out more like a conventional speedo but is driven by the road speed sensor that is part of the EFi system. If the road speed sensor fials you may get an EFi warning light and on later models the air suspension will go into limp mode too. The cruise control will also not work.
The original hot-wire had the sensor for the EFi and a mechanical speedo, so there are 2 cables, the sensor is a drive-through unit fastened to the N/S chassis leg, on later models the output is just blanked. Later the cabel and sensor were replaced by a smaller sensor in the gearbox itself, I'd only expect to see that on a softdash.
So, the most common fault on a mechanical is likely to be the angle drive at the back of the speedo head or a cable that has slipped to one end. Typically this may be proceded by the speedo jumping at low speeds.
An electronic speedo could be the speedo head or the speed signal which is processed by a unit the size of a flassher relay and IIRC is white. Don't ask me where it is at this time of night though :roll:
