+Tachometer / RPM gauge
Somehow I was focused early on getting the Tachometer / RPM meter to work. Reading various sources on the internet it appears BMW varies its method to send the engine speed signal to the cluster. Some are CAN based, others are frequency based signals. Luck struck me, my RPM gauge is frequency driven! I can remove the entire petrol engine ECU & wire loom.
For those familiar with BMW Z3 / e36 series, it is pin 20 on the X20 connector. The breadboard is only used for a tiny NPN transistor to amplify the scope generator output.
488Hz produces about the same result on the Instrument cluster. The digital debug mode shows a slightly different RPM than the needle.... It not exact but its fair enough.