Dirk, die Signale, die in das KI kommen, werden verarbeitet, siehe Seite 6
http://www.e38.org/e32/BMW_pdfs/INST_info.pdf
Speedometer: signals from the rear axle reed contact are supplied to the instrument cluster, where they are transformed into speed proportional current.
Tachometer: the analog signals come from the DMEcontrol unit. The frequency is converted into indicator deflection by the cluster circuit board.
Check erst mal was Haschra vorgeschlagen hat, dann geht es weiter step by step.