Are you sure you mean aux fan, or ACC blower fan? Blower is outside fuse box in front of and near the fender in a small black casing. Aux fan should be in the fuse box, unless MBZ has changed the location for the 500E.

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.