A mirror assembly security system for a vehicle includes an exterior mirror assembly and a light module removably positioned within the exterior mirror housing. The light module is moisture impervious and includes an enclosure, a light-emitting opening in the enclosure, a light source in the enclosure radiating light through the light-emitting opening, and a cover for the light-emitting opening adapted to direct the light from the light source to an area adjacent the vehicle to create a security area. The light source may be supported by a pair of electrical contacts provided on the inner surface of the enclosure. The enclosure wall supporting the electrical contacts is preferably flexible, in order to allow the light source to be captured by the contacts. Attachment of the cover adds rigidity to the enclosure to prevent further flexure of the enclosure wall in order to firmly retain the light source. The enclosure is preferably configured so that the same unit can be installed in both left and right handed exterior mirror assemblies even though the light module generates a non-symmetrical light pattern. A reflective surface is provided in the enclosure which cooperates with the cover to produce a generally collimated light pattern.