Instrument Cluster

The speedometer, tachometer, and fuel economy guages on my 88 325i convert. don't work. The on board computer calculates the average speed, fuel usage and mileage, but nothing on the instument cluster.
I checked the voltage and ground as per the Bently manual, and this checks out. Any Ideas?

check for input signals from dme (engine computer) if car runs then dme is reciving signals from cranksensor and working properly but signal may not be making it to cluster. does your manual give a wiring scematic of cluster?

does the heater fan and the back up lights work??? if they don't, check the fuses, check them good..

Indicator light, two semi circles aroungd a circle with an exclaimation oint in the middle, what does it mean, I have no owners manual

check for input signals from dme (engine computer) if car runs then dme is reciving signals from cranksensor and working properly but signal may not be making it to cluster. does your manual give a wiring scematic of cluster?
yes,the bently manual has a wiring schematic, but it is vague. the way I understand the system is as follows; The RPM sensor is on the front of the engine. The signal then passes to the motronic control unit (DME). The car will not run if there is no signal here, and the car runs fine. From there the control unit sends the signal to the on board computer (systems monitor and fuel economy unit).The on board computer uses the RPM signal along with the ground speed to estimate fuel economy/efficency.The on board computer seems to be working also because it gives me all the information it is supposed to, so I assume it is receiving the signal. but the tach. and the analog miles per gallon gauge in the speedometer doesn't work. The bently manual doesnt tell me what kind of a signal I am supposed to have so I don't know if it is millivolts/resistance, pulse or what.

does the heater fan and the back up lights work??? if they don't, check the fuses, check them good..
Yes they all work and I took the 21 poiunt connectors off of the back of the instument cluster an checked for volts/ground per the Bently manual and it all checks so it could not be a fuse.

het brian that is your brake linings light it means your pads are low.

Changed instrument cluster, same problem.
HELP!
Does anyone know if the speed signal goes anywere else after it leaves the on board computer.
Cruise control? Fuel pump?
Where does the computer get fuel rate input information? Motronic DME? If so where does the DME get the information? Could this be related to my problem?
Should I go to BMW service and grab my Knees.
Been there, they are not very gentle.

As it turns out( if anyone is interested) the service indicator board batteries are the culpret.
The tach. and fuel economy guages operate from signals that first pass through the service indicator board. If the batteries or service indicator board are bad, or if either are replaced and not enough time allowed for the batteries to recharge, the tach. and fuel economy guages will not work. Although, if the batteries are good, they may come to life later when they charge.