Aiming and Adjusting Automotive Headlights

Adjusting automotive headlights is an operation that should make its way onto every motorist’s routine maintenance schedule. Properly aimed headlights will provide the driver with the best possible nighttime view by assuring the correct distance and width is illuminated ahead of them. Another often overlooked fact is headlights that are out of adjustment can create hazardous conditions for other drivers if your headlights are pointing at their face instead of the road in front of you. This article will cover the procedures and pitfalls to avoid when aiming an automobile headlight.

Leveling the Vehicle

Whether you are just quickly checking the aim of the headlights or performing a specific adjustment the importance of having the vehicle level cannot be overstated. As an example if 100 pounds of load is placed in the trunk of a standard four-door sedan this could raise the front headlights, 2 to 4 inches above the point measured with no load in the trunk. Even an automobile heavily coated with snow or ice can affect the riding height. For these reasons an adjustment shouldn’t be made unless the vehicle is clean and empty of unusual loads.

Another important item to consider is tire inflation. If the left front tire is 3 to 5 pounds per square inch less than the other side it can cause misalignment of the headlights by a few inches after the tire pressures are corrected. Also affecting ride height would be the condition of the struts, shock absorbers or springs for the vehicle suspension. If this vehicle has a lot of miles and these parts are original equipment, ride height should be checked to verify the measurement is within specifications.

Checking the Headlight Aim

A good auto repair shop will have an optical headlight aimer that makes quick work of verifying the most intensive area of the beams are pointing where they are supposed to. Although this equipment can cost between 500 and $1000 I’ve seen used ones from closed down repair centers on popular auction sites for around $100. For drivers wanting to avoid the use of specialized equipment a general check can be achieved by using a projector type screen chart set up about 25 feet in front of the headlights. A garage door or sheet of plywood is perfect for setting up target points.

The aiming marks can be drawn on paper and taped to the garage door or plywood. The vehicle should be 25 feet away from the targets. The bull’s-eye on the targets is achieved by making a few measurements. First measure the distance between the center points of the headlight bulbs. Then draw a vertical center line halfway between these two measurements. Next you measured the distance from the ground to the center of the headlights and subtract about 2 inches for the distance away from the targets and draw a horizontal line. This will provide you with a cross-hair where the concentrated beam should focus.

Making Headlight Adjustments

The headlight bulbs fit inside of an assembly that is often called a bucket. This allows for the independent movement of the beam focus to be adjusted in any direction. Adjusting screws are provided to move the bucket in the desired direction to correct the main focus point. Lateral or side to side adjustments should equal the distance the headlights are apart from each other. Vertical or up-and-down adjustments are critical in how far ahead the driver can see at night. It is important to note that headlights that are set too high can shine in the face of approaching drivers. Therefore aiming a little low is better than aiming a little high.

Some manufacturers believe that the aiming and adjustment of the headlights is so important that they include the equipment necessary to make all adjustments right on the headlight bucket assembly. Two companies known for doing so is Chrysler and Mazda. Many of Their headlights are equipped with a bubble level to aid in vertical headlight alignment, plus a horizontal gauge with a magnifying window is located next to the bubble level to aid in horizontal adjustments.

The important take away from this article is that proper headlight adjustment will help the driver see the maximum distance ahead of the vehicle in nighttime driving situations. This adjustment is equally important to drivers that share the road with you. As an example if the left front headlight is aiming high and to the left this will shine directly into the face of oncoming drivers and can temporarily blind them as you pass by.