A rearview mirror assembly for a vehicle comprises an electro-optic mirror unit whose reflectivity is variable in response to an electrical voltage applied thereto and an electrical circuit for controlling operation of the mirror unit in response to one or more light sensors. A bracket for supporting the mirror unit from an interior portion of the vehicle via interengaging ball and socket members allows angular adjustment of the mirror unit. The ball member includes a plurality of electrical contacts on a convex surface thereof for sliding engagement by respective counter-contacts over a range of angular movement of the mirror unit for supplying power to the electrical circuit from a vehicle electrical system external to the mirror assembly.