My 1992 960 has an ongoing problem with an erratic speedometer which sometimes works and sometimes does not. When it does not work, the tranny is confused and erratic, hunting gears.

I've replaced the sensor in the diff and checked all wiring, including solder joints on back of the inst cluster. I'm convinced the problem is within the inst cluster, and would like to replace it, but I cannot find one from a 1991 or 1992. I can find good ones from 1993, and they look the same, ie, same connectors on the back.

Does anyone know whether the 1993 will work, or, does anyone know of a source for a 1992 cluster?

 

It's my understanding that the speed signal is split before the instrument cluster, so I still think you have an issue with either the sender or wiring from it.
See if you can borrow an analogue multimeter and measure the signal coming from the speed sensor.

Regards, Andrew.

 

I don't know a lot about automatic transmissions, but I never knew that they relied at all on the signal to the speedometer.

 

If that's the case, it should be an easy fix. Do you know where I can find a wiring diagram?

 

No. I'd try trolling the internet or perhaps a workshop manual.
Another way would be to follow the speed signal wire backwards from the instruments, the split on most all cars is usually fairly close to the instrument panel. If you know where your transmission computer is, you should be able to figure out roughly where the wire is split off.
I had a Nissan that was doing this sort of thing, several places could not diagnose it and wanted to swap computers, sensors etc.
I spent a day tracing wiring and found the splice to the instrument panel was bad.

Regards, Andrew.