A broken tail light or brake light is a traffic ticket waiting to happen and a serious safety issue – vehicles behind cannot tell when you are slowing down. Replacement is one of the simplest electrical jobs you can do, though access varies significantly between vehicles. This guide walks through diagnosis, replacement, and what to do when LED lights fail.
Diagnosing a Dead Bulb
Have an assistant press the brake pedal while you stand behind the vehicle and look at the rear lights. All brake lights should illuminate brightly and evenly, including the high-mounted centre brake light (CHMSL) typically mounted on the rear window or boot lid. Repeat the test for tail lights (with headlights or parking lights on – these should be a dimmer constant glow), reverse lights (shift into reverse with the engine off and ignition on), and indicators on each side.
A single dead bulb usually means just that bulb has failed – the filament has burnt out from age or vibration. Multiple bulbs out at once suggests something more systemic: a blown fuse, a poor ground connection at the light assembly, a wiring fault, or a problem with the body control module. Always start with the simplest cause – a single bulb – before tearing into electrical diagnosis.
Access to the Light Assembly
Most tail light assemblies are accessed from inside the boot. Remove the trim panel or access cover (often held by plastic clips or fasteners that turn 90 degrees) to reach the back of the light assembly. On some vehicles, you twist the bulb holder out of the back of the housing – a quarter turn counterclockwise typically releases it. On others, the entire light assembly unbolts from the outside via two or three fasteners (often hidden behind plastic plugs in the boot opening). Your workshop manual shows the exact procedure for your specific model.
Bulb Replacement Procedure
Once you have access, twist the bulb holder a quarter turn counterclockwise and pull it out of the housing. Pull the old bulb out of the holder – most modern wedge-base bulbs just pull straight out, while older bayonet-base bulbs need to be pushed in slightly and twisted before they release. Inspect the contacts for corrosion or signs of overheating (a black or melted bulb base is unusual and may indicate a wiring issue causing excessive current).
Fit the new bulb, ensuring it is the correct type. Common rear bulb types include P21W (single filament 21W stop or indicator), PY21W (amber single filament for indicators), P21/5W (dual filament 21/5W for combined stop/tail), W21/5W (similar wedge-base), and W16W (smaller wedge for reverse on some vehicles). The bulb itself or your workshop manual will list the part number. Refit the holder by aligning and twisting clockwise, and test all functions before reassembling the trim.
Halogen vs LED Replacement Bulbs
LED “replacement” bulbs in halogen housings are popular but problematic. The optical pattern is designed for the specific shape and position of the halogen filament; LEDs scatter light differently and can reduce brightness in the direction the housing is designed to project. Many LED bulbs also draw less current than the original halogen, causing the body control module to detect a “bulb out” warning. Load resistors can mask this but add complexity. For brake and tail lights specifically, if you have halogen housings, halogen bulbs typically remain the safest choice.
LED Tail Light Failures
Many modern vehicles use LED tail lights with the diodes integrated into the housing. These are not user-serviceable – when individual LEDs or the driver circuit fails, the entire tail light assembly typically needs replacement, which can cost hundreds of dollars even on mainstream vehicles. Some manufacturers sell replacement LED modules separately but many do not. Check warranty status if your vehicle’s LED tail lights fail – some manufacturers extend coverage on known-failure-prone designs.
Bulb types, access procedures, and connector pin assignments are vehicle-specific. MechanicMate offers PDF workshop manuals for over 960 models with complete electrical and lighting information at mechanicmate.net/shop.
— MechanicMate . Questions or a second opinion? [email protected].