Brake light problems

I noticed that my new car has issues with the brake lights. The Service Indicator Lights (SIL) indicate that there's a problem with the brake light circuity ("Bremsli. Elektri" it says), and first I went and checked the fuse #1.

Even though it appeared fine, I replaced it, and the brake lights started to work okay. Good. But, after driving a while and parking to a gas station, I noticed the same message again. I checked the fuse #1 again, and it was fine. After riding home, the lights worked fine for an instant, but then broke again. Must be bad wiring then.

Oh, in case you are wondering, my BMW 525iA is from the year 1991, so I would say it's a E34 model with the M50 engine.