During a long trip in US West (hot and dry) in last year, I drove my car into a one-mile tunnel with my family. The headlight didn't turned on automatically as expected. The car went into darkness. I tried to turn on the headlight manually. It didn't response. I braked my car in the dark tunnel. I was wondering if I should make an u-turn inside the tunnel. As I saw a car from the opposite direction coming with it headlight, I scared to death. I also prayed that the driver behind me would be on alert. After all the attempts in panic, I finally figured out that high-beam headlights are still working. With manually turning it on and off, I managed to get throguh the long tunnel. After that, I reversed my trip plan, and came back home earlier.
I had thought I just had bad luck and the headlight control system became defected in the critical wrong time. But as I came back to California (normal weather conditions), the headlight work normal again. This is obviously a electronic component reliability problem in dry heat environment. If a car hit behind us in the dark tunnel, no one would know the accident was cause by a failure from Benz. As I came back home, I tried to see if there are any recall from Benz on the headlight, and found no thread. I am still using the same headlight for almost one year without further problem. Of cause, I dare not drive the same car to the US West again.