BMW Repair: 92 325ic Tachometer/computer, gauge cluster, board computer

Question
I have a 92 325ic with a non-functioning tachometer (including the mpg indicator). The on-board computer also is not working.

The other electricial systems all appear to be working.

Is it a bad connection? If so, where do I look?  

Answer
It could be the reference sensor connection behind the starter and under the intake manifold.  It's also possible the sensor is bad.  It's also possible the gauge cluster is shot; since the computer gets it's info from the tach it also would be affected.
-cheers
[email protected]