Abstract: A brush wear detector comprised of an L-shaped leaf spring having the outer end of its longer leg mounted on a first insulating member in fixed relationship to a spring support for a self-winding, brush-biasing spring. A second dielectric member is secured to the leaf spring between the ends thereof and projects outward from the leaf spring into engagement with an uncoiled section of a brush-biasing spring. The free end of the leaf spring is held away from engagement with the brush-biasing spring support, thereby being electrically isolated from it, when a new brush is mounted in operating position under the brush-biasing spring. When the brush becomes worn a pre-determined amount the brush-biasing spring moves in a direction away from the second dielectric member and so enables the leaf spring to force its free end into electrically conducting engagement with the electrically energized spring support.