It might be the wiring. I believe the coupes were spared, until 1993 from the biodegradable harness. I know my 1992 300CE was.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).