Aftermarket housings will most likely have a sharp cut-off line on the top of the beam. The idea is to get max projection without the main part of the beam in oncoming drivers' eyes or in the mirrors of the car ahead of you. You want the main part of the beam to be declining from the bulb downwards. The after market housings can be tricky to get a happy medium between good projection without blinding other traffic.

With the car on level ground, at night turn on the lights and stand about 10' in front of one beam. Look at your pants and discern the top 'cut off' line. Put you finger on your leg to mark the spot, and start walking towards the beam. You want the cut off to be rising on your leg as you approach the car. If it is falling, the beam is too high.  You want the left beam slightly lower than the right beam, again for max visibility forward, without blinding oncoming traffic. Mark one beam on your leg, and walk across to the other beam, and compare the height. Right should be slightly higher. From 10' out, you want about a 2"-3" difference.

For side to side, you want left hand straight ahead, or very slightly to right of c/l,  and right a bit to the right.  You can wave your hand in front of the beam and watch the pattern of the shadow on the ground, or block the opposite light your working on with a piece of cardboard to check the side to side pattern.

You can crounch down in front of the beam, move your head back and forth and up and down to find the "hot spot" of the beam, and gauge if this point is physically higher/lower, right,left, or center of the lens to gauge your alignment. Adjust as necessary. I use the pant-leg for height, and looking for the hot spot for side to side. Then look at the pattern on the ground, and evaluate the results while driving for final validation.

And a last check while driving: As you pull up to a light behind a big, flat rear vehichle like a suburban, expedition, or pick-up that is already stopped, watch the location of the top cut off of the beam on the rear of the vehicle. As you approach it, the cutoff should rise slightly as you get closer. If it stays the same, or falls, the lights are adjusted too high.

The best way is trial and error, and understanding what you want the final pattern to be. Further out you can get it without blinding oncoming traffic. There's some tips I've come up with from decades of adjusting headlights.

Check your repair manual for the detailed step by step instructions of adjusting headlights.  Apparently using a blank wall with the car 25' from it and the use of masking tape is the least preferred method.  Some of the repair manuals I have recommend going to a shop using headlamp alignment equipment and recommend the aiming be checked during bulb replacement, when a wheel alignment has been done, or after collision repairs have been made.  They also recommend the car be empty with a 1/2 a tank of gas.  The Haynes Repair Manual gives you a very good diagram of the manual set up.  The GM Factory Repair Manual gives you both methods but doesn't favor 1 over the other diagrams on each.  Note: some states have specific requirements for headlamp aiming.

|UPDATED|1/12/2014 2:02:44 PM (AZT)|/UPDATED|