The lights on your vehicle serve three purposes: They allow you to see, they allow you to be seen, and they allow you to signal other drivers of your intentions.

When you have a light that doesn't work, no matter if it is a parking light, brake light, or headlight, it can be dangerous, and it can also lead to a traffic ticket.

How To Check the Various Lights On Your Car

  1. Check all external lenses for cracks - a cracked taillight allowing white light to spill out can quickly lead to a ticket.
  2. Visually check all accessible wiring connectors, harnesses and retaining clips under the hood, in the trunk, and elsewhere for security, and for signs of chafing or damage.
  3. To check your brake lights and blinkers unaided, back up to a wall and operate the lights. The reflected light on the wall should be enough show if they are working properly.
  4. If a single indicator light, brake light or headlight has failed, it is likely just a blown bulb that will need to be renewed. If both brake lights in a system have failed, it is likely a fuse or the switch.
  5. To replace a fuse, locate the fuse box (under the dash, in the engine compartment, or in the trunk), pull the old fuse, and replace it with one of the same rating.
  6. A blown fuse can indicate a bigger problem, but it can also just indicate a fuse that has aged due to vibration and heat.

Your Haynes manual will have wiring diagrams of the lighting circuits, as well as the location of the fuse box for any electrical troubleshooting you may need to do.

The Different Types of Lights

The Front of the Car

At the front of your car, there are usually five different types of light.

First, are the parking lights, which can be used when visibility is slightly reduced to help people see you. In recent years, these have been replaced or combined with Daytime Running Lights (DRL), which come on automatically as soon as the vehicle’s ignition is switched on, and go off when the headlights are activated.

Also up front, sometimes sharing a lens or even a bulb with the parking lights/DRL, are your turn signals, which you activate to let people know you are about to turn or change lanes.

The headlights are next, with both low and high beams. The low beams is used any time visibility is compromised by the darkness of night, or by adverse weather such as rain, fog or snow. The high beams, sometimes called the brights, are the brightest lights at the front of the car, and should be used only when there are no other vehicles in front of you. It is also useful to flash the high beams to get the attention of a driver in front of you.

Some cars also have a pair of front fog lights located low to the ground, below the fog. These have a wide light beam spread so they illuminates the road the area immediately in front of the car all the way to the curbs at the edge.

The Rear of the Car

At the back of every car are red taillights, which are illuminated whenever the headlights or parking lights are on. Some cars also feature low mounted red fog lights in back, which help you to be seen in heavy fog and snow. The brake lights are the same red as the tail lights, and often in the same unit, but are brighter and are only illuminated when you press the brake pedal.

Sometimes combined in the same unit as the brake and taillights are the rear turn signals. These are usually red as well in America, but some European and Asian cars have them in amber, and flash to alert drivers behind you of what you are about to do.

Also out back are one or two, white "back-up" or reverse lights, which help you see behind you when reversing at night, but also signals to others that your car is about to move in reverse.

Taillights glow in the darkness

Different Types of Bulbs

All of these lights have traditionally been powered by incandescent bulbs, at least since gas lamps fell out of favor in the early 20th century. However, some manufacturers have moved on further, and now offer LED lights, which are brighter and longer-lasting, yet consume less energy and produce less heat, so can be packaged much tighter.

In the past 20 years, some higher end cars have used high voltage, bright, long lasting HID or Bi-Xenon headlights, many of which aren't considered user serviceable. Finally, some car makes are now launching laser headlights, which promise to be the future of brightness and efficiency.

Halogen/Filament Bulb

Until recently all headlights were filament bulbs, and operated in the same way as a regular household bulb with electrical current heating up a thin metal filament.

Most bulbs are now filled with halogen gas which allows the bulb to run hotter and therefore brighter. In some cases bulbs are filled with xenon gas (not to be confused with HID xenon headlights) which give a whiter, brighter light. In older vehicles, and some commercial trucks and vans, the bulb is sealed in a unit with the headlight lens, which is why they are called “sealed beams”.

Turn signals, parking lights, taillights, reverse lights, and others also commonly use filament bulbs, although they are steadily being replaced with LED units. 

HID/Xenon and Bi-Xenon

HID stands for High Intensity Discharge, and they don't have a filament like regular bulbs, instead the light comes from an arc of electricity that jumps across two electrodes within a xenon filled glass tube.

These lights require a small box of electronics that both starts the light and controls its output, called the ballast. The ballast boosts the voltage to several thousand to make the arc, then dials it back to hundreds of volts to maintain it. Often a car equipped with HID lights will still use a halogen bulb for the high beam, or passing light, or a combination of HID and filament lights.

HID lights are brighter and whiter and generally last longer (around 2000 hours), but are sometimes considered "not user serviceable" due to the voltages. The bulbs cost considerably more than regular bulbs, but replacement isn't any more complex. 

LED

LED stands for Light Emitting Diode, and due to their low power usage and ultra long life LEDs are increasingly used within headlights, taillights, and turn signals.

LED headlights are typically only used as the low/high beam on newer cars, and hybrids, but they are becoming more common. LEDs are increasingly being used for blinkers, brake lights, fog lights, and more, and may last the life of the car in these applications. 

Aftermarket replacement LED bulbs which replace many old style bulbs are also available for retrofitting, but due to their low power consumption they can cause issues. You may get warning lights on your dash indicating a blown bulb, or the turn signals may not blink properly. If this occurs, a "CANbus LED" with a tiny resistor built in to simulate the power usage of a normal bulb may solve it. LED turn signal bulbs that don't flash properly can also be fixed with resistors, or the installation of an electronic solid state flasher/blinker relay.