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.