MB Stars, thanks again. I found the relay. I determined I could get the center illumination to work by jumping the #1 and #2 sockets on the connector. That tells me the problem the connection behind the ashtray is good. I suspect the problem is that #4 has a bad connection at the instrument cluster or the relay itself is bad. I guess I should check #4 for continuity. Thanks for your help.

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2005 Mercedes C230k sport sedan, 6 speed
1987 Porsche 924S - 968-engined track car