I am not sure about Mercedes, but a lot of cars have "dummy", or empty fuse slots. Some cars of the same make/model are equipped with certain options/features, and rather than making seperate fuse boxes for them, they just put the same fuse box in all of them. I am not sure what the auxillary fan is though.

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2004 Toyota Sequoia Limited 4wd
1991 Lincoln Town Car Executive
1991 Cadillac Sedan DeVille
1988 Mercedes 300SEL
1972 Chevrolet Caprice Kingswood Estate 9-passenger wagon
1973 Pontiac Grand Ville
(Prior MB's: 1974 240D, 1985 380SE, 1984 190D, 1993 400SEL)