1987 260E low beams keep blowing fuse
 

On my 1987 260E, the low beams keep blowing their fuses. The high beams and other lights work fine. (not sure about dashboard lights b/c they were dim to start with). I've only had the car a couple of weeks and purchased it from a family friend who didn't mention any problem other than the dim lights on the dash (I now know about the dimmer switch, but haven't had a chance to check if that works as I've only had it out a couple of times in the evening and the low beam fuses blew each time.) The car was always kept in a garage and fully maintained. Any ideas or suggestions?

Thanks,
Denise