You don't state what year, but for the E39 (1997 - 2003 MY) there is one in the trunk on the left side in the battery compartment and another in the glovebox.
The Early 90's BMW 525 series 1st fuse box is located under the hood and can be found easily in front of drivers side. The second is behind the drivers side rear seat bottom..Give it a good tug on...