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It might be a central grounding issue, check the service manual and locate the grounding points through the dash and check them (based on the systems that are going haywire (lights). The service manual is a long read but you may find it compelling to see what the schmatics indicate for the systems that are (again) lighting up the dash. Good luck! BTW, an independent european mechanic with SLK series MB's, may have an answer (from experiences already solved).

NEVER GO TO A DEALERSHIP TO FIX A CROSSFIRE!


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