Repair Guide: Lights, Fuses & Flashers

Modern vehicles use dozens of bulbs to light everything from the road to the ashtray. Servicing the system is easy; over half of all lighting problems are caused by burned out bulbs, corroded sockets or burned out fuses.

The first step in understanding a vehicle's lights, fuses and flashers is to learn about basic electricity. For more information on electrical circuits, how they work and how to troubleshoot them, please refer to the information on "Understanding and Troubleshooting Electrical Systems" elsewhere in this manual

Light Bulbs
See Figures 1, 2, 3 and 4

Small bulbs, used for most automotive applications, come in several basic types-single contact bayonet base, double contact bayonet base with opposed or staggered indexing lugs, cartridge types for a small, flat installation, and wedge-base light bulbs.

Small bulbs show a broken filament when burned-out and are easily replaced. Turn them about ¼ turn and pull them from the socket. The single contact bayonet base is usually used for instrument panel lights in a small snap-in socket. The major difficulty in replacing these is finding them.

The double contact bayonet base is commonly used for turn signals, parking and taillights. The staggered indexing lugs allow one-way installation so the filament connection is correct. These bulbs are reached by removing the lens or light assembly; inside the trunk is also a common place to hide the light housings.

Don't forget to install the gasket under the lens or housing, if one is used. The gasket seals out moisture, a major cause of bulb troubles. While the bulb is out of the socket, check the socket for corrosion and if necessary, clean it.

Poor grounding is a major cause of non-functioning bulbs, especially when the bulb filaments are OK. Scraping the terminal sockets and polishing the bulb contacts is frequently all that's required. Also, check the ground between the bulb housing and the fender, and between the fender and the body. The electricity has to get back to the ground (negative) side of the battery. If it can't because of poor grounding, the bulb won't work. Many times, running a ground wire from the bulb housing directly to the frame of the vehicle is easier than trying to make a ground through rusted sheet metal.

Figure 1 Examples of various types of automotive light bulbs

1. Halogen headlight bulb
2. Side marker light bulb 3. Dome light bulb
4. Turn signal/brake light bulb


Figure 2 Burned bulbs show a broken filament (arrows)

Figure 3 Depress and twist this type of bulb counterclockwise, then pull the bulb straight from its socket

Figure 4 Disengage the spring clip which retains one tapered end of this dome light bulb, then withdraw the bulb



Headlights
See Figures 5 and 6

In the good old days, headlights where the one part for the vehicle that were easy to figure out. They were round sealed beams and you either had two or four mounted on the front of your vehicle. Nothing stays simple very long. New styling brought on rectangular headlights. This alone doubled the number of possibilities. Even more design changes and lowered hood lines brought out the small rectangular and even the mini-quad (the smallest size sealed beam). This brought the possible number of sealed beam configurations to seven.

For years, European vehicles used halogen capsule headlight assemblies. It wasn't until the late 80's that the Department of Transportation (DOT) approved the use for these in U.S. vehicles. This added three new possibilities to the existing sealed beams. However, what this meant to the automaker's was that they could design composite aerodynamic headlight assemblies that could conform to every body design and they can share these common replaceable halogen capsule bulbs.

Practically all late model cars and light trucks use halogen lights. The halogen lights increase the candlepower of the headlight from 75,000 to almost 150,000 and boosts the distance a driver can see at night by almost 20% over the old tungsten lights. Automaker's started installing them on top-of-the-line models in 1980 and they went to wide spread use on 1981 and later models.

Like the old tungsten lights, the halogen lights use a tungsten filament, but it is contained in a halogen gas environment, which allows the filament to be heated to a much higher temperature to produce a much brighter and whiter light. They also require less power, so that a smaller and lighter alternator can be used.

See Figure 5 Common headlight configurations


Figure 6 Light patterns of different types of headlights

HEADLIGHT REPLACEMENT

See Figures 7, 8, 9 and 10
On most vehicles, light bulb replacement is a simple matter. On sealed beam units, the retaining ring is removed (by loosening the clamp and/or removing the retaining bolts), then the beam is pulled forward so the electrical connector can be unplugged.

Figure 7 To replace most sealed beam headlights, start by loosening the retaining ring fastener(s) . . .

Figure 8 . . . then remove the retaining ring to free the headlight

Figure 9 Pull the lamp forward and unplug the wiring harness, then install the replacement bulb

On most halogen vehicles the bulb is replaced from behind the lamp assembly. Usually it is just a matter of opening the hood, unscrewing the lock ring on the bulb socket and/or the bulb socket itself and withdrawing the assembly from the back of the lamp. Once the socket is exposed you can remove the old halogen bulb and install the replacement.


NEVER touch the glass of a halogen bulb! If you touch the glass, you fingers will leave behind natural skin oils which will create a hot spot on the bulb, burning it out LONG BEFORE the natural end of its life. Most halogen bulbs contain a metallic coated tip which can be safely handled and, of course, you can always handle it by the plastic base.


Figure 10 Most new vehicles require only halogen bulb replacement


AIMING THE HEADLIGHTS

See Figures 11, 12, 13 and 14
The headlights must be properly aimed to provide the best, safest road illumination. The lights should be checked for proper aim and adjusted as necessary. Certain state and local authorities have requirements for headlight aiming; these should be checked before adjustment is made.


About once a year, when the headlights are replaced or any time front end work is performed on your vehicle, the headlights should be accurately aimed by a reputable repair shop using the proper equipment. Headlights not properly aimed can make it virtually impossible to see and may blind other drivers on the road, possibly causing an accident. Note that the following procedure is a temporary fix, until you can take your vehicle to a repair shop for a proper adjustment.


Headlight adjustment may be temporarily made using a wall, as described below, or on the rear of another vehicle. When adjusted, the lights should not glare in oncoming car or truck windshields, nor should they illuminate the passenger compartment of vehicles driving in front of you. These adjustments are rough and should always be fine-tuned by a repair shop which is equipped with headlight aiming tools. Improper adjustments may be both dangerous and illegal.

For most of the vehicles, horizontal and vertical aiming of each sealed beam unit is provided by two adjusting screws which move the retaining ring and adjusting plate against the tension of a coil spring. There is no adjustment for focus; this is done during headlight manufacturing.

On vehicles with composite headlights, the assembly is bolted into position, no adjustment should be necessary or possible. Some applications, however, may be bolted to an adjuster plate or may be retained by adjusting screws. If so, follow this procedure when adjusting the lights, BUT always have the adjustment checked by a reputable shop.

Before removing the headlight bulb or disturbing the headlamp in any way, note the current settings in order to ease headlight adjustment upon reassembly. If the high or low beam setting of the old lamp still works, this can be done using the wall of a garage or a building:

1. Park the vehicle on a level surface, with the fuel tank about ½ full and with the vehicle empty of all extra cargo (unless normally carried). The vehicle should be facing a wall which is no less than 6 feet (1.8m) high and 12 feet (3.7m) wide. The front of the vehicle should be about 25 feet from the wall.
   
2. If neither beam on one side is working, and if another like-sized vehicle is available, park the second one in the exact spot where the vehicle was and mark the beams using the same-side light. Then switch the vehicles so the one to be aimed is back in the original spot. It must be parked no closer to or farther away from the wall than the second vehicle.
   
3. Perform any necessary repairs, but make sure the vehicle is not moved, or is returned to the exact spot from which the lights were marked. Turn the headlights ON and adjust the beams to match the marks on the wall.
   
4. Have the headlight adjustment checked as soon as possible by a reputable repair shop.
   
5. If aiming is to be performed outdoors, it is advisable to wait until dusk in order to properly see the headlight beams on the wall. If done in a garage, darken the area around the wall as much as possible by closing shades or hanging cloth over the windows.
   
6. Turn the headlights ON and mark the wall at the center of each light's low beam, then switch on the brights and mark the center of each light's high beam. A short length of masking tape which is visible from the front of the vehicle may be used. Although marking all four positions is advisable, marking one position from each light should be sufficient.
   

Figure 11 Location of the aiming screws on most vehicles with sealed beam headlights

Figure 12 Example of headlight adjustment screw location for composite headlamps

Figure 13 Low-beam headlight pattern alignment

Figure 14 High-beam headlight pattern alignment