Cadillac 2004 DeVille Owner's Manual page 333

4. Turn on the low-beam headlamps and place a
piece of cardboard or equivalent in front of the
headlamp not being aimed. This should allow only
the beam of light from the headlamp being
aimed to be seen on the flat surface.
Notice: Do not cover a headlamp to improve beam
cut-off when aiming. Covering a headlamp may
cause excessive heat build-up which may cause
damage to the headlamp.
5. Turn the vertical aiming screw (C) until the
headlamp beam is aimed to the horizontal tape line.
The top edge of the cut-off should be positioned
at the bottom edge of the horizontal tape line.
6. Repeat Steps 4 and 5
for the opposite
headlamp.
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