A tail light is part of the exterior lighting system on a motor vehicle. Modern automobiles feature a tail light assembly that combines a number of different lights into a single assembly. Actually, cars, trucks, and SUVs have a pair of tail light assemblies, left and right. Mounted at the rear of the vehicle, the tail light assembly typically houses the brake lights, running lights, reverse or “back-up” lights, and turn signals.
Inside a tail light assembly are multiple light bulbs that respond to various vehicle conditions. The running lights are red and allow other drivers to see your vehicle from behind in the dark. Brake lights are also red and come on whenever the brake pedal is pressed. The reverse lights are white and turn on when the transmission has been shifted into reverse. And the amber-colored turn signal on one side or the other will light up when the turn indicator is activated. If a driver switches on the hazard lights, the turn signal lights on both tail light assemblies will flash.
Years ago, tail lights consisted of a collection of separate lights mounted at the rear of a vehicle. Modern vehicles, however, feature assemblies that combine several lights into two single housings, one on the left and one on the right. The housing itself is made up of a plastic inner shell into which the lights are mounted. An electronic circuit board might also be included.
The outer face of the assembly is also made of plastic, a transparent lens through which the lights can shine. A portion of the lens is red (brake/running light), another amber (turn signal - although the turn signal bulb might be amber and shine through a clear window), and another clear (reverse light).
If the lens is cracked or broken - or if its surface has oxidized so that the lights no longer shine through clearly - your tail light assembly might need to be replaced. Otherwise, under normal circumstances, it is common that only a bulb needs to be replaced when it burns out.
For instance, if a brake light is not working, it may well be that the brake light bulb has burned out. In that case, a technician might install a fresh bulb in place of the failed one. Same goes for any of the other lights in the assembly.
It should be noted, however, that some newer vehicles feature LED tail lights that are not serviceable and require that the entire assembly be replaced rather than a bulb.
You will know that a tail light assembly needs service if any of its functions do not work properly - running, braking, turning, or reversing. You might also notice a warning light on the dashboard. If a turn signal bulb is bad, the signal might click or blink faster than normal.
To replace a tail light bulb, a technician will identify the bad bulb, access the back of the assembly, dislodge the failed bulb, unplug it from the wiring harness, and insert a new bulb. Access to the assembly differs from one vehicle to the next. In many vehicles, the technician can access the bulbs through the trunk or cargo compartment by removing an access cover. On other vehicles, it may be necessary to remove the assembly from the vehicle first before dislodging the bulb.
Most tail light assemblies are bolted in place. A technician must access the mounting hardware from inside the vehicle. Special clips are often included as supplemental fasteners, and a technician must take care to avoid breaking the clips or the hardware to which they are attached.