Your vehicle's third brake light, also called the center high-mounted stop lamp or CHMSL, is federally mandated safety equipment on all cars sold in the U.S. since 1986. Driving without it is illegal in all 50 states and can result in traffic citations, fines, and potential vehicle inspection failures.
The CHMSL sits at the top of your rear window or trunk lid and functions as a redundant braking signal. When you hit the brakes, this light alerts drivers behind you alongside your two lower brake lights. The federal motor vehicle safety standard requires this third light precisely because it provides better visibility and reduces rear-end collision risk, especially in poor weather or at night.
If your CHMSL burns out, you have a legal obligation to replace it promptly. Law enforcement can pull you over specifically for this violation. Fines vary by state but typically range from $50 to $150. More problematically, a failed brake light will cause your vehicle to fail state inspection in most jurisdictions, preventing you from renewing your registration.
Replacing a third brake light is straightforward and inexpensive. Most vehicles take 15 to 30 minutes. You'll access the light from inside your trunk or cargo area, unscrew the housing, and swap out the bulb. Replacement bulbs cost $5 to $15, and many auto parts stores install them for free with purchase. Some newer vehicles use LED units that may cost more to replace but last far longer than traditional bulbs.
Ignoring a burnt-out CHMSL creates unnecessary legal and practical headaches. Beyond fines and inspection failures, you're reducing safety margins for drivers behind you. The third brake light system exists because automotive data shows it prevents accidents. Keeping yours functional takes minimal time and money.