GMC PD-4103 Maintenance Manual page 141

GM COACH MAINTENANCE MANUAL
Sec. 7
Page 133
tor damaged, the complete unit must be replaced.
With switch marked "HEAD" on panel turned
on, headlight and fog light circuits are energized.
The headlight or fog light circuit is then selected
by the foot-operated selector switch on toeboard.
When headlights are used, upper or lower head-
light beam is selected by the foot-operated dim-
mer switch on toeboard. Tell-tale light on gauge
panel marked "HI BEAM" illuminates when head-
light upper beam is being used.
Proper Use of Headlights
Headlights are designed to provide adequate
highway lighting for normal operating conditions.
The headlights will provide safe lighting, provid-
ing they are aimed correctly, equipped with proper
Sealed-Beam units, lens are clean, and upper and
lower beams are used correctly.
1. Upper Beam. High beam should be used
only on unlighted roads when no approaching ve-
hicles are near.
2. Lower Beam. Lower beam should always
be used when approaching another vehicle. The
depressed beam provides safer road visibility than
upper beam under passing conditions, providing
both vehicles use the depressed beam.
3. Headlight Lens. Dirt on lens absorbs a
considerable amount of light. Clean lens with
water and a good glass cleaner whenever dirty.
4. Headlight Wiring. For maximum illumina-
tion, proper voltage must be obtained at the bulb.
Discharged battery, loose or dirty electrical con-
tacts in wiring system, and poor ground connec-
tions all contribute to a decrease in voltage. Check
wiring and connections regul~rly, make sure gen-
erator is charging sufficiently, and keep battery
properly charged.
Sealed-Beam Unit Replacement (Fig. 30)
Headlight Sealed-Beam unit may be replaced
in following manner:
1. Remove rim retaining screw and remove
rim.
2. Remove three retaining screws.
. 3. Pull Sealed-Beam unit out of light body,
disconnecting wiring as unit is removed.
4. Insert prongs of new Sealed-Beam unit into
wiring plug, then position unit in light body.
5. Install Sealed- Beam unit retaining ring and
attach to light body with three screws.
6. Install door with clip engaging slot at top
of light body. Install door retaining screw at bot-
tom of door, tightening screw firmly.
Headlight Adjustment
Headlights must be aimed carefully and ac-
curately to assure safe vehicle operation at night.
Adjustments can be made quickly and accurately
LIGHTING SYSTEM
HEIGHT
TO
CENTER
OF
HEADLIGHT
CENTER LINE AHEAD OF
RIGHT HEADLIGHT
POSITION OF COACH WITH RESPECT TO SCREEN
TP 0091•1
Figure 31-Headlight Aiming Chart
with a headlight tester, but if such equipment is
not available, adjust lights as follows:
1. Position vehicle on level floor with head-
lights 25 feet from a vertical wall or door as
shown in figure 31. Vehicle center line must be
perpendicular to vertical surfacB.
2. Draw a horizontal line on vertical surface
at height of light center as shown in figure 31.
Locate a point on this horizontal line at which
projected center line of chassis intersects. Meas-
ure distance between light centers and divide the
distance equally on either side of center mark.
Then draw a vertical line directly ahead of each
light center as shown.
3. Switch on high or bright beam in headlights
and cover one light while adjusting other.
4. Remove door retaining screw (fig. 30), and
door for access to adjusting screws. Top screw
provides vertical adjustment and side screw aims
light horizontally.
5. Beam pattern should approximate that shown
in figure 32. A distorted beam pattern is usually
caused by a sprung reflector, in which event
Sealed-Beam unit must be replaced.
6. After headlight is properly aligned cover
its beam and proceed in same manner a; above
with opposite light.
HOT SPOT
TP 0092-2
Figure 32-Headlight Beam Pattern