Blower motor won't shut off. I know for a fact that the push button control unit is working fine. So why won't it shut off? Fuses are fine....where else do I look?

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1973 280 - Sold
1980 300SD - Sold
1982 240D - Stolen
1988 300E - Sold
1989 260E - Sold
1989 560SEL
1994 E420 - Sold
1997 E420
2005 CL500