Mercedes Forum - Mercedes Benz Enthusiast Forums - mercedes have a problem in rain

If this is really the case, and it appears that moisture (rain, etc.) are affecting the electrical system somehow, then you need to try to isolate the area where it is happening. One way to do this is to open the hood of the car and get the garden hose out and turn it on a low stream, so it doesn't splash around a lot. Then, VERY carefully, and only in one SMALL area starting at the front of the engine, put a little water on it. If nothing happens, move to the next area. Listen carefully for any change in the sound of the engine, sputtering, missing, etc. If you hit the area that is affected, it should start doing what it does when it rains. After all, what's the difference. This way, at least you have isolated the particular area or part that is the problem. Then you can deal with it accordingly. But the trick is to find out what it is that's being affected by the water. Go slowly. Very slowly. It may take a minute for the part to react. Good luck.

PS> This is also the trick to finding leaks in a car. I did this for 15 years as a glass worker. We would put somebody inside the car (or trunk!) and slowly wet a SMALL area of the car starting from the BOTTOM UP. If you don't start from the bottom up, you will never know where it's leaking because the water you put on it will simply run down the rest of the car and you are right back to where you started with no clue where it's coming in. When the water is visible in the car, the person in the car knocks loudly on the doorglass to signal visible water coming in at that particular spot. Simple.