Tail lights, so named for their rearward facing location on the tail end of a vehicle, are an essential safety feature that indicates a vehicle's location to approaching traffic. Tail lights are usually small incandescent or light emitting diode (LED) bulbs encased in a waterproof plastic housing in the rear deck of the car, truck or motorcycle. To amplify the light output, tail light enclosures usually include reflective material that magnifies the light, making it appear larger and brighter. Tail lights are usually red or clear in color, though many states regulate the specific color of tail lights and restrict the use of clear tail light housings. Finally, tail lights may be augmented by turn signals, brake lights, back-up lights or other lighting fixtures specific to the make and model of vehicle.
To operate effectively, tail lights must illuminate at night and in poor weather conditions. Since drivers are mainly concerned with front-facing visibility and rarely think about the rear of the vehicle, manufacturers tie the tail light illumination to the operation of the headlights; when a driver turns on the headlights--or, as is common in newer vehicles, when a light sensor activates the headlights--the tail lights automatically illuminate as well. This automatic activation is achieved by placing the tail lights on the same relay as the head lights; in essence, tail lights are wired to the same switch that activates the headlights, causing them to come on anytime the forward-facing headlamps are activated.
In some situations, a driver needs to use the headlights and tail lights when the vehicle is not running. For this reason, the headlights--and, thus, the tail lights--are wired directly to the vehicle's battery. In a normal configuration, wiring connects the negative (ground) lead of the headlights and tail lights to the vehicle chassis and ultimately back to the negative terminal of the vehicle battery. The positive wiring leads are connected first to a switch, then a separate wire lead connects the switch to the battery's positive output. When the switch is in its normal position, it leaves an opening in the electrical circuit, and the lights remain off. When the driver (or, as mentioned above, a computer) activate the switch, though, the circuit is completed, and both the headlights and tail lights illuminate.
As described in above, tail lights serve the purpose of indicating the rear edge of a vehicle to oncoming traffic when ambient lighting is not sufficient for approaching drivers to accurately gauge the shape and size of the vessel. To help avert potential accidents, state and federal regulations mandate tail lights on cars, trucks, motorcycles and any other vehicles that use public roadways. If a tail light should burn out, become damaged or otherwise cease to function, the driver of the affected vehicle may face an increased risk of accidents; to help ensure the driver is aware of the situation, most states and municipalities require law enforcement officers to pull over the driver and issue a warning or citation.
