Rgnprof, you are probably aware of the need to maintain the ignition system meticulously. If, for whatever reason, you haven't then it's possible the ICU (mounted on the driver's side inner fender) has failed. The easiest way to confirm is installing a known good one temporarily. The ICU (or EZL) is very expensive ... Around $2,500 when I bought one for our 1992 300CE.

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Fred Hoelzle