Its your fuse, eventhough it appears O.K., it is not. Same thing happened to my E 320.
The fuse appeared perfect, but changed it for a new and it solved the problem. Just change the fuse for a new one.
By the way, a good rule of thumb is changing ALL fuses on your fuse box every 6 to eight years. Not costly at all, and it will save you a lot of headaches.
CL 500, 1998
S 500 L, 1998
E 320 T, 1995