How often have you had to brake suddenly with another driver right on your tail? Your eyes dart to the rearview mirror, hoping he'll see your brake lights in time.

But what if your brake lights aren't working properly? There's better than a 50/50 chance they're NOT, according to figures from a survey by American Automobile Club of Cleveland, OH. They found 55% of vehicles checked had brake lights that needed some kind of repairs. This was by far the most prevalent mechanical discrepancy found during a Car Care Clinic.

Bob Knop, manager of the Club's Approved Auto Repair Department, which conducts the clinics, says most problems were found with the brake light, generally because of a burned out bulb.

"We've grown to depend on lighting to signal our intentions," says Janine Sine, Manager for the G.E. Automotive Lighting Division. "We respond almost subconsciously to fellow motorists' turn signals, brake lights or emergency flashers. It's a form of communication as vital to driving as road signs and center lane marking. When they're missing we're unaware of the danger ahead."

Another common lighting problem, according to Sine, is found on vehicles with four light systems with separate units for high and low beams. Because the high beam lamps are replaced less often the lens is subjected to years of abuse from pebbles and other road debris. Eventually hair-line cracks develop and moisture works its way inside, corroding the reflector. The unit may appear to be working OK but it is not putting out as much light as it should.

"Some day it may be widespread practice in the U.S., as it is in Canada and Sweden, that headlights be turned on whenever the car is driven. It's a proven safety measure and already is the law in the U.S. on two wheeled vehicles where lights automatically turn on with the ignition switch. Obviously, they are more visible to other drivers," says Sine.

"An Avis traveler safety study showed vehicles with daytime running lights (DRL) had a better accident record than vehicles not so equipped."

But lights are worthless if they are not working, Sine emphasizes. All exterior lights should be checked periodically, not only for burned out bulbs and flashers but also for poor illumination of headlamps due to damaged reflectors.

The best way to check your system is to have one person turn on the lights, the emergency flashers and turn signals and apply the brakes while someone else walks around the vehicle to see that everything is working.

It's also a good habit during every gas fill-up to check for dirt (and ice) on all lenses, front and rear. To help maintain cleanliness you can apply a glass treatment such as RAIN X^(TM) to help repel rain, sleet, and snow.

At one time or another most of us have been blinded by the glare of oncoming headlights. You flash your high beams to signal the oncoming driver to dim his lights. He responds by turning on his high beams, indicating it was his low beams that had been blinding you. They were aimed too high.

Are you sure your headlights are not blinding others? Here, from G.E., is the recommended way to check headlight aim.

1. Put your car on a 35-40 foot stretch of flat or evenly sloped pavement such as a driveway facing a wall or garage door.
2. Shine your low beams on the door from 2 to 3 feet away and outline the bright spots on the door with a pencil or tape.
3. Back the car to about 25 feet from the door. The top of the low beams should shine no higher than the top of the marks on the door or lower than the center of the marked circle. If your vehicle has four headlights the center of the high beam (the inner or lower two lights) should align with the top of the low beam marks. If you have only two headlights, the high beams are automatically aimed when you aim the low beams.

For most accurate aiming take your vehicle to a professional. If, on the other hand, you're a "do-it-yourselfer", follow these instructions from G.E.:

1. Remove the outer trim for access to the adjustment screws. To raise the beam turn the top adjustment screw clockwise; counter clockwise to lower the beam. Turn the side adjustment screw clockwise to move the beam to the right and counterclockwise to move it to the left.
2. Bring each beam into its final position by turning the adjusting screws clockwise so the headlamp will be held against its tension springs when the operation is completed.

If your lights continue to be out of adjustment, consult a service technician.