I had the same problem and posted a request for help here. Someone suggested fuse number 5 and I checked, also checked rotated all fuses to improve contact. After spending time and money trying to solve this problem it turned to be fuse number 6, these fuses can have hairline breaks and I sure missed it even when looked " carefully " check all your fuses. before you waist any money, Mine is a 1990 300SE fuse #6 was the magic.