Cut-off mechanisms for a motor vehicle headlight activated by an electromagnet with two gaps comprise a movable assembly that comprises a cut-off bar and a movable element, as well as an actuator motor comprising an electromagnet, the movable element being movable under the action of the electromagnet, against a return spring, between a near activation position and a remote rest position relative to a ferromagnetic core of the electromagnet, the movable element being configured to create an interruption in the continuity of a magnetic circuit formed by the ferromagnetic core, a metallic casing and the movable element, when said element comes near to the ferromagnetic core in the activation position.