A control for a moisture sensing assembly, adapted for mounting on the inner surface of a vehicle window or windshield to control vehicle accessories such as windshield wipers, maximizes the window area being sensed in relationship to the size of the assembly and provides immunity to interference from environmental influences. In the preferred embodiment, moisture on the outer window surface is detected by first and second moisture sensors each including infrared energy radiating diodes and radiant energy detectors which detect and process radiant energy to produce a moisture signal that is a function of the moisture on the window. A synchronizing circuit intermittently actuates the radiating diode for the two sensors individually and alternatingly at equally-spaced intervals. The synchronizing circuit also inhibits the radiant energy detectors from processing the radiant energy signal except when the corresponding radiating diodes are emitting energy in order to prevent interference from the other radiating diodes and environmental influences. The synchronizing circuit includes a pair of oscillators which include capacitors and coupling devices that coordinate the discharging of the capacitors in a manner which provides equal intervals between alternating output pulses from the oscillators.