How To Replace Tail Light Bulbs

Lights on automobiles serve two functions: vision and visibility. Headlights and fog lights give the driver vision. Tail lights give the driver visibility to those behind him. In addition, tail lights are used to signal those behind the car of the driver's intentions. Tail lights come in four classes.

Running Lights

The running lights in the rear of the car are always red in color. In the early days of motoring they were the only lights on the rear of the car. Running lights consist of a bright light at the extreme corner of the rear, and a small light on the side of the car. This small light is known as a side-marker light, and is intended to make the car visible from the side. Modern cars have tail lights that wrap around the corner of the car, making the additional lamp unnecessary.

Running lights are on whenever the headlights are on. In cars with "daytime running lights" in the front, the running lights may be lit at the same time. The important function of running lights is to alert following traffic of the car's presence at a greater distance, day or night.

Brake Lights

Brake lights are brighter than running lights. Their purpose is to warn the following driver that the brakes are being applied and the car is slowing. Brake lights supply useful information to the car behind and are used day and night. Brake lights are situated in the same location as the running lights. Cars built in the last twenty-four years are also equipped with a "high mount stop light." The high mount stop light is a brake light mounted on the centerline above or on the trunk lid. It comes on with the regular brake lights, providing an additional warning to following cars.

Turn Signals

Turn signals are also located on the rear corners of the car. In older American cars they operated by blinking the brake light. Modern cars use a separate lamp for the turn signals. European cars have an amber lens over the turn signal bulb, instead of red. This configuration, required by law in Europe, has been adopted by American manufacturers. The turn signal blinks on the side towards which the driver intends to turn. They also blink in unison when the "hazard flasher" is on.

Tag Lights

The tag light is a small bulb or bulbs next to the license plate. It is illuminated when the running lights are on. It's intention is to permit law officers to read the license plate at night. If it is out, the driver can count on getting pulled over.

Replacing Tail Light Bulbs

No standard method exists for attaching lights to the rear of a car. European manufacturers are conscientious about making the changing of bulbs easy. In European winter, the nights are long. European countries have strict lighting standards, requiring drivers to carry replacement bulbs with them at all times. The tail lights in European cars are accessed through covers located in the trunk.

American cars are not so simple. Some have bulbs that can be accessed through the trunk. Some have bulbs that can be accessed after the lens is removed from the outside. On many, the entire tail light assembly must be removed to access the bulbs. Camaros built in the eighties, for example, have a tail light assembly spanning the entire rear of the car which must be removed. It is a good idea to consult the owner's manual before changing the bulbs for the first time.

High mount stop lights can be mounted inside the rear window, on the parcel shelf. In American cars this means that they have to be serviced from inside. Japaneses cars using this mounting position access the bulb from the trunk below. Consulting the owner's manual is, once again, a good idea. Tag lights present the same problem and the manual should be consulted.

The Tail Light Bulb Itself

How to Replace Tail Light Bulbs Thirty years ago there were only a half-dozen bulbs used by all the manufacturers. Today, more than fifty are used. Running light, turn signal, and brake light bulbs are all similar. Bulbs used for these purposes are bright, and have large bases. Prior to the mid-eighties, all of these bulbs had round metal bases. The bases have small studs on them which engage slots in the sockets that receive them. The bulb is pushed into the socket against the tension of a spring and twisted clockwise to engage the studs with the grooves. The configuration of the studs, and the contacts on the base of the bulb, is unique to each type of bulb.

The bulbs with round metal bases use those metal bases as their ground circuit. When computers and other electronics became more common in automobiles, designers were forced to stop using the bodywork as part of the ground circuit. The bulb manufacturers designed new bulbs with isolated circuits and plastic bases. Plastic-based bulbs are held in place with tiny tabs protruding from the base near where they attach to the glass envelopes. These tabs vary with the manufacturer of the car.

Removing the bulb from the socket is simple. Metal-based bulbs are twisted counter-clockwise and pulled straight out. Plastic-based bulbs have tabs that are squeezed to release them from their sockets. Plastic-based bulbs will need to be rocked back and forth to get them out of their sockets, which have a tight grip on the contact strips. Inserting the new bulb is a reverse of this process.

The Socket

The manufacturer of the car fills the socket with insulating grease before inserting the bulb. The grease is to keep moisture out of the socket. When replacing the bulb, the old grease is removed from the socket. It dries and is an obstacle to making a good connection with the new bulb. A dab of new grease on the base of the new bulb will keep the socket water-proof.

Hazards

The biggest hazard present in the changing of these bulbs is broken glass. Bulbs can require a great deal of force to disengage them from their sockets. Older metal-based bulbs are the worst, due to corrosion between their bases and the metal of the sockets. It is always a good idea to wear gloves when performing this chore. If the bulb does shatter before coming out, a large screwdriver blade inserted into the base will give enough leverage to twist it out. Needless to say, the lights and ignition should always be in the "off" position when working on anything electrical.

Finishing Up

When reinstalling the light assembly, or closing the compartment in the trunk, it is important to make sure that they are sealed. Even with grease in the sockets, water is not welcome in the tail light housing. If the lens is cracked, or the gasket around the assembly torn, a new one must be installed. Silicone sealer can make a temporary repair, but water will work its way in when the silicone dries.

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