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 are a being sensed while minimizing the size of the overall assembly. In the preferred embodiment, moisture on the outer window surface is detected by stacked rows of infrared energy receiving sensors spaced in angular relationship from stacked rows of infrared energy emitting diodes. The emitter diodes and sensors are preferably carried in separate emitter and detector mounting blocks slidably fitted in a rigid carrier. The sensor row closest to the window receives energy from the diode emitter row farthest from the window and vice versa. Energy barrier walls are provided in the diode and sensor support for blocking energy reflected by the inside window surface. The assembly is adapted for use with an electrical circuit which operates one emitter diode row and its corresponding sensor row while the other emitter and sensor rows are deactivated to prevent interference and false reflected signals from the other emitter row. Removable attachment to the window with a circular member provides ease of installation and improved positioning and orientation of the sensing assembly.