An auxiliary third brake light which is installed on a truck bed enclosure or frame is disclosed. The auxiliary third brake light is not physically secured by adhesive or mechanical fastener to the truck bed, cab or body or any part of the truck. The parts of the auxiliary third brake light mounted to the truck bed cover and contact the truck bed, cab or body is pressed into contact. When the truck bed cover is collapsed or removed, the user can have full use of the truck bed. The parts of the auxiliary third brake light that contact the truck bed, cab or body are pulled off therefrom. When the truck bed cover is deployed to the erected position, the parts of the third brake light that contact the truck bed, cab or body are properly repositioned back into position.