I think the part # varies by model and year. Mine was a gray box with a red lid and a 10 amp fuse inside the lid on the firewall next to some other black relay boxes. I placed the order with my friendly Mbz parts dept at the dealership where I work, and they handed me one the same day. This is not a catch-all cure, but it has seemingly worked for me.

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2002 Ford ZX2
2 x 2013 Honda Civics