Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
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No, a construction problem is not known here.
It may well be that the connector on the wiring harness side is defective or leaking. There are two possibilities to solve the problem. Either you or the garage can get a suitable plug from a used wiring harness (from a car from the car recycling company) or the entire wiring harness would have to be replaced.
Since the wiring harness is very expensive, replacing the plug would be the preferred option.
I think from your description that the plug either does not seal properly in the front where it is plugged together, or very likely from the back where the cable goes in. There the cable is equipped with a round rubber seal just before the contacts. If this seal is not correctly seated or was damaged during installation in the factory, water will always come through here.
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