Category: Cars, Products

The 2005 GMC Sierra 1500 is a durable and hardworking truck, but it has a well-known weakness: the third brake light (CHMSL – Center High Mount Stop Light) mounted above the rear window. Over time, the factory foam gasket that seals this light to the cab roof deteriorates due to UV exposure, heat cycling, and simple age. When this gasket fails, water pours into the cab during rain or car washes, running down the back wall, soaking the carpet, and potentially damaging your audio system, power window switches, or even the body control module. Replacing the third brake light with a new unit and installing a proper seal is essential maintenance for any 2005 Sierra owner. This guide walks you through the process and shows you how to permanently stop cab leaks.