June 16, 2021

How To Aim Headlights

Written by: Scott Julian of XK Glow

Improperly adjusted headlights on a semi truck can be a serious problem. It’s tough to see when driving at night and you may be inadvertently blinding other motorists as your pass by. There are many reasons why your headlights may be out or alignment ranging from a recently installed set (such as new XK GLOW LED bulbs) to worn suspension. Understanding how to check and adjust your headlights will help you to stay safe out on the open road.

Why Aligning Headlights Matters

Whether you are working on Freightliner, Mack or Peterbilt 389 headlight adjustment, the first question you may be asking is why it matters. There are a few important reasons for getting the adjustment right.

Perhaps the most immediately obvious reason is that your headlights need to be pointed correctly to illuminate the road before you. If your headlights are pointed too low, you will not have enough visibility to react if you spot something on the road such as a deer or debris. If they are too high, you may not be able to fully see what is close to your truck, making tight maneuvering difficult.

The next most significant reason is that your lights can blind other drivers. If you have ever been on the receiving end of improperly adjusted headlights, you know how much they can impede your vision. This is not only annoying to other drivers, but it is also very dangerous.

Finally, there are rules set by the National Highway Traffic Safety Administration that govern the glare allowed by headlights. While it is unlikely to get a ticket for accidentally misaligned lights, you may be looking at trouble with the law if they are particularly egregious. In short, it just makes sense to align them properly. It is safer for everyone and it’s the law.

How To Know When Your Headlights Aren’t Adjusted Properly

When your headlights are improperly adjusted to a significant extent, it is obvious. It is clear that they are not illuminating the road the way that they should. Additionally, you will likely hear some angry horn honks from drivers who have been blinded. However, it may not be as obvious when the problem is minor.

In fact, alignment issues may happen more often than you realize. Factors such as cargo weight, suspension wear and improper tire pressure can cause them to get out of alignment.

The best way to ensure that your headlights are properly adjusted is to periodically check them. This should include whenever you make modifications to your truck or repair it after an accident. You can simply follow the process described below but not make any actual adjustments.

Let’s get started!


Phillips head screwdriver or Torx wrench Masking tape
Tape Measure Level ground
Wall with 25ft of clearance  


How To Adjust Headlights on a Semi Truck

The process for adjusting headlights is more or less the same for every truck. So, if you’ve learned how to adjust Peterbilt headlights, you know how to adjust International headlights. Nonetheless, it is a good idea to consult your owner’s manual. This will include details on how to adjust the angle of the lights.

Locate the Lights and Adjustment Screws: Check your owner’s manual to find the location of the vertical and horizontal headlight adjustment screws. These screws are typically long and feed into gears that control the headlight adjustment. They are usually marked L > R for horizontal adjustment and U > D for vertical adjustment.

Prepare Your Area: Find a level surface in front of a garage door or wall with a minimum of 25ft of space. We will use the 25ft mark as a reference so you will need enough space for your vehicle to fit behind that line. Using the tape measure, measure 25ft back from the wall and mark that line using masking tape.

Check the Close Alignment: Park the vehicle against the wall and turn on the low beam headlights. Using masking tape, create a plus sign at the center of the headlight beam. The two strips should mark the horizontal and vertical centers of the lights. These should be level with one another. Take your time to get your mark right.

Check the Distant Alignment: Back vehicle up in a straight line until the headlights are at the previously taped 25ft mark. The difference between the close and distant aim will help you to align your headlights.

Adjust Horizontal Aim: At 25 feet, the horizontal center of the beam should still align with the taped vertical centerline from the close measurement. Use the horizontal adjustment screw to adjust for the centerline.

Adjust Vertical Aim: At 25 feet, the vertical center of your headlight beam should be one to two inches below where it was when parked close to the wall (marked by the horizontal strip of masking tape). Use the vertical adjustment screw to adjust the height of the headlights as necessary.

That’s all there is to it. Go for a drive and enjoy your properly aimed headlights!

Get High-Quality Headlights for Your Semi Truck

Now that you know how to adjust your semi truck headlights, consider upgrading to a high-quality set of LED lights. Having powerful and long-lasting lights will help to keep you safe on the road.

Truck drivers choose XK Glow brand headlight bulbs because they are reliable to light up the road night after night with superior light output and durability. They’re the highest quality LED bulbs on the market and are proven to withstand rough terrain, harsh vibration, and intensive use. Our top-selling XK Glow Elite LED Headlight Bulbs provide a customized look with practical functionality. Owner-operators say that these are the best LED headlight bulbs they have ever used!

Shop for the best headlight bulbs for semi trucks today. Then, put your new headlight aiming skills into practice.

Questions, comments, or concerns? We’re here to help! [email protected] or [email protected]

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