Got it. Where did you get the ECU? They appear to be totally unavailable even from Mercedes?

I have the Starfinder and wiring diagrams at my shop - do you have access to them? Haven't researched it but I think the starter motor signal comes through the front SAM and utilizes a cube relay to provide the actual starter solenoid signal. I believe the ECU initiates the signal but I'm not sure.

Could be as simple as a flaky relay. Or it could be much more complicated.

Let me know if you want me to dive into the schematic for the starter circuit.

TIm

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