Abstract: An electro-optical liquid detector assembly comprises a support block having a flat front surface attached to the internal surface of a wind-shield and being formed therein with a pair of inclined bores opening toward the internal surface of the wind-shield, a transparent flat plate contained within the support block and fixed to the support block to form a common flat front surface with the support block, the transparent flat plate being formed in its rear surface with a pair of spaced v-grooved portions which are opposed to the inclined bores, a light emitting element disposed within one of the inclined bores to emit a beam of light into the wind-shield through one of the v-grooved portions of the flat plate so as to cause internal reflection of the beam between the external and internal surfaces of the wind-shield, and a light receiving element disposed within the other inclined bore to receive the incident beam reflected by the external surface of the wind-shield through the other v-grooved portion of the