Headlight Adjustmet "How To's"

[truckster]

You need level ground, a wall, and a tape measure. You should also have a full tank of gas, but that will make more of a difference in a Blazer or a Suburban than a truck, because of where the tank is located.

At 25 feet from the wall, the top cutoff of the beam should be the same height as the top of your headlight. The left cutoff should be straight ahead of the left edge of the truck. The right headlight should meet the left headlight's right cutoff. That's about all there is to it.

[theastronaut]

The low beam pattern needs to drop 3" over 25 feet. If the beam pattern doesn't drop then ANY incline will make your headlights shine up into oncoming traffic. Measure from the center of your headlight to the ground, and subtract three inches. Find a level spot and park 25 feet from a wall, then mark the wall at that height with masking tape. Has to be very level since you're only dealing with a .60 degree angle. The top of your low beam pattern needs to be just under the tape line. If you have sealed beams than the light pattern will be a "blob" of light that can make aiming more difficult- there won't be a defined line where the upper half of the low beam pattern stops off. If you have H4 headlights that are E-code, you'll have a sharp cut off on the top half of the low beam pattern that makes aiming easier.

Here's a diagram.




Here's a shot that compares the E-code pattern (left) to SAE/sealed beam pattern (right side). You can see that the E-code makes a sharper line for easier aiming, and less glare for oncoming traffic.