In a rain sensor system for a motor vehicle, a sensor element is provided as separate part for attachment in the vicinity of a vehicle window. The sensor element is wiped by a separate wiper blade which is fastened to a windshield wiper or driven by the latter. As a function of the a degree of wetness present on its top, the sensor element supplies electric signals to an evaluation electronics. Above a limit value of the signals, the evaluation electronics connects the windshield wiper.