Yes. A center high-mounted stop lamp (CHMSL), commonly known as the third brake light, is required on most modern passenger vehicles in many regions and enhances braking visibility. If your vehicle is older or imported, check your local laws and inspections to confirm requirements.
This article explains what a CHMSL is, whether you legally need one depending on where you live, and how to install or replace a CHMSL safely and legally if your vehicle lacks one or you want to upgrade your signaling. We also cover common installation pitfalls and maintenance tips.
What is a center high-mounted stop lamp?
Below are the essential characteristics and safety purpose of CHMSLs:
- Stands for Center High Mounted Stop Lamp, or the third brake light.
- Typically located centrally at or near the top of the rear window or the trunk lid.
- Activates with the brake pedal to provide a higher, clearer brake signal to drivers behind, especially in heavy traffic or for taller vehicles.
- Most modern cars include a CHMSL; older vehicles may not.
- Color is usually red and must meet local brightness and visibility standards.
In short, a CHMSL is a safety feature designed to improve the visibility of braking signals for drivers behind you.
Do you need one by law?
Regulatory requirements vary by country and region. In many places, all new passenger cars and light trucks are required to have a CHMSL and to maintain a functioning unit during ownership. Retrofits may be allowed but are subject to standards and inspections. Always verify with your local motor vehicle authority before making changes.
Below is a high-level pattern of how requirements tend to work across regions:
- New vehicles: CHMSL is typically mandated and must be present at purchase; the lamp must be visible and functional.
- Older vehicles: Some jurisdictions require retrofits only when the vehicle is brought into service after a certain date or during safety inspections; others may allow continued use if existing lighting remains compliant.
- Aftermarket replacements: Allowed in many places if the unit is designed for automotive use, properly wired to the brake signal, and meets brightness/color standards; non-certified or improperly installed units may fail inspections or be illegal.
- General safety principle: You must have functioning brake lights, including the CHMSL if required by law; a non-functional CHMSL can lead to tickets and liability in an accident.
Bottom line: check with your local DMV or equivalent authority to confirm whether your vehicle must have a CHMSL and whether any retrofit is allowed or required.
How to install or retrofit safely
Choosing a compliant lamp
Identify an automotive-grade third brake light that meets the standards in your region (for example DOT/SAE in the US, or ECE in Europe). The lamp should be designed for rear brake use and offer adequate brightness and color conformity.
Below is a list to guide the selection process:
- Look for official markings such as DOT/SAE (US) or ECE (EU) to indicate compliance with regional standards.
- Ensure the unit is designed for brake-activated use and provides a consistent, bright signal when braking.
- Prefer units with weatherproof housings and sealed wiring to withstand road conditions.
- Avoid novelty or non-certified aftermarket lights that may not meet safety standards.
- Verify compatibility with your vehicle’s mounting points and electrical system.
Choosing a compliant lamp helps ensure the retrofit remains legal and visible to other drivers.
Mounting and wiring
Before you begin, plan the mounting location, alignment, and wiring to minimize interference with the vehicle’s weather sealing and to ensure safe operation.
- Mount the lamp at or near the vehicle’s centerline and as high as practical without obstructing the rear window or trunk.
- Wire the lamp to the brake light circuit so it activates only when the brake pedal is pressed; use proper wiring, fusing, and load management.
- Use weatherproof connectors and grommets; route wiring away from moving parts and heat sources.
- Test the unit from typical following distances and confirm that it activates with braking and remains off when brakes are not engaged.
- Consider professional installation if you are unsure about electrical integration or compliance with local inspections.
Proper mounting and wiring ensure the CHMSL functions reliably and remains legal.
Maintenance and safety tips
Keep the CHMSL clean and unobstructed, and periodically check for brightness, alignment, and electrical performance. Replace expired lamps promptly and address any moisture or condensation inside the unit.
Summary
Most drivers will encounter a CHMSL requirement through new-vehicle regulations, and many regions require retrofitting only under specific conditions. If your car already has a center high-mounted stop lamp, maintain it and keep the rear area clear of obstructions. If your vehicle lacks a CHMSL and you plan a retrofit, choose a compliant, automotive-grade unit and have it installed properly to meet local laws and safety expectations. Always verify regional rules with your local authority before making changes.