Buick 1998 Century Owner's Manual page 293

If
you find that the headlamp aiming needs adjustment,
follow these steps:
Driver's Side Headlamp Shown
A. Vertical aim adjustment screw
B. Horizontal aim adjustment screw
1. Start by opening the hood and locating the vertical
and horizontal aim indicators. The aiming screw for
the vertical aim indicator is at the center of the
headlamp cover (A) and the aiming screw for the
horizontal aim indicator is on the outboard side of
the headlamp cover (B).
I
NOTICE:
Horizontal aim of the headlamp must be done
first. Adjusting vertical aim first will result in
incorrect headlamp aim.
Passenger's Side Headlamp Shown
B. Horizontal aim adjustment screw
C. Horizontal block index plate
D. Vertical aiming level
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