In DOT-speak, that stands for Center High-Mounted Stop Light, ie the 3rd brake light. Has anyone added one to the back of their camper? As far as I know there are no laws requiring one, but the safe...
I have never seen a box truck or enclosed trailers with one . It might interfere with the 3 center marker lights . Usually the brake lights on a camper or truck are higher than cars with 3rd brake light . Interesting