6 A center high-mount stop lamp (CHMSL), or more commonly called a third brake light, is a known safety enhancement that all cars have been built with since 1986. Adding one to your classic Mustang is a good idea and can be had several ways. One simple way is a pre-made package tray with the light built in. We’ve also seen custom LED strips mounted at the top of the rear glass. For our project, we flush fit a 12-inch LED strip into the Shelby decklid for optimum visibility.