Did you take the time to read the output voltage of the alternator?

Light on typically indicates low voltage which is common as the internal regulator begins to fail.

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1971 280SL ROADSTER
1988 300CE TWIN TURBO WIDEBODY
1994 E320 CABRIOLET
1999 C43 AMG
2005 G55K AMG
2008 CLK63 AMG BLACK SERIES