I have a 518i SE; E34; 1992.
Instrument CLuster problem = tachometer and speedometer have no reading, no movement at all.
All fuses OK
Most wiring I have inspected is OK.
Replaced capacitors on cluster circuit board.
Cluster has Grey back; two connectors BLUE and YELLOW.
Removed Car security / immobiliser as it was shorting - may have affected instrument cluster before identified and removed security.
Seems like a power issue to cluster meters - BUT
my question is: do the two meters (speedo and tach) have common power supply or circuitry that may cause them both to go at the same time?
Speed sensor in rear differential BUT this does not make sense repairing as I thought the tach must take a reading from engine RPM and thus, not common to both.
Please let me know if anyone has advice or same problem ... rest of instrument cluster fine EXCEPT resets (lose all readings occasionally) but I know this is to do with cluster battery as I had same problem in my 318i (1987) EXCEPT on the instrument cluster board for the 318 there was a AA rechargeable that could be replaced do not know what and where the cell that has same purpose exists for my 518.
Thanks. Hope that gives the experts all required info.