Known by several names - the third brake light, high-mount light, center mount light, and, officially according to the law, “center high mount stop lamp” or CHMSL, the center brake light is a lamp mounted at the rear of a vehicle, higher than the normal brake lights and in the center. The light comes on whenever the driver presses on the brake pedal.
Studies show that a brake light placed higher and more prominently at the rear of a vehicle helps to prevent rear end collisions. Therefore, since 1986, vehicles in North America have been required to have a center brake light.
Signs that a center brake light needs to be replaced are fairly simple and straightforward. If you or someone else notices that the light is not coming on when the brake pedal is pressed, the light probably needs to be replaced. In most modern vehicles, a dashboard warning light or status indicator will also reveal a bad brake light, be it a standard brake light or the center brake light.
In some cases, a failed center brake light might be caused by a blown fuse or problem with the wiring. In those cases, the light would not necessarily need to be replaced.
The procedure to replace a center brake light depends on the specific vehicle make and model. Most cars place the center brake light above the package tray or rear deck, just below the rear window. Vehicles with hatchbacks or liftgates might have the light mounted inside at the top of the gate window or outside, mounted in a spoiler. Trucks often feature a center brake light at the top of the tailgate.
In general, a technician will need to remove any covers that are in the way of access to the bulb or assembly. The light is unfastened and dislodged, and the bulb is replaced. If the light is LED, the entire light assembly might need replacement.