in rainy weather the alternator stops

Mercedes Benz A class 2002
Hello
in rainy weather the alternator stops filling or weakens, whereas in dry weather everything is fine.
Has anything happened to anyone?

Could this be a result of something turned on due to the rainy weather, such as do you notice the change when your lights, or wipers are first turned on? If so possibly short in wiring somewhere or old wiper motor needs replacing perhaps. Have you monitored the voltage compared to normal vs when it is as you say stops working?

Belt slipping, is alternator near water spray?