Outlined below are service procedures covering
lights used on typical S-Series vehicles. Some vehicles
may be equipped with additional accessory lights which
are not covered herein.
When diagnosing light failure, first check for a
"blown" fuse or tripped circuit breaker. Fuse sizes and
locations are listed in the circuit diagram section of the
Truck Service Manual Refer to the appropriate section
covering the model year of the vehicle being serviced. If
a "blown" fuse or tripped circuit breaker is found, inspect
wiring circuit for cause of overload and make necessary
If fuse or circuit breaker is satisfactory, check for
"burned out" light bulb and replace if necessary, Light
bulb types used in various lights are listed in the LIGHT
BULB CHART in this section.
If light bulb is good, check wiring and connectors
for an "open" circuit. A 12-volt test light can be used to
check circuit continuity. Refer to the appropriate wiring
Various types of headlight aiming equipment are
available commercially. When using aiming equipment,
Where headlight aiming
available, headlight aiming can be checked by projecting
the upper beam of each light upon a screen or chart at a
distance of about 25 feet ahead of the headlights. The
truck should be exactly perpendicular to the chart.
The vertical lines on the chart (Figure 1) mark
the distance between the vertical center lines of the
headlights and are equally spaced from the center line of
Fig. 1 Headlight Aiming Pattern
Pattern (Upper Beam)
Center of Truck
A horizontal line should be placed on the chart at
a level of two (2) inches below the height of the headlight
centers above the floor.
With headlights on "HIGH" beam, the "hot spot"
of each projected beam pattern should be centered over
the point of intersection of the vertical and horizontal
lines on the chart, as shown in Figure 1.
If necessary, adjust headlights vertically and/or
laterally to obtain proper aim. (See HEADLIGHT
Headlight aim should always be checked on a level floor
with the vehicle unloaded,
In some states, the above instructions may conflict with
existing laws and regulations. Where this is the case,
legal requirements must be met,
Modify the instructions accordingly.
Adjusting screws are provided to move the
headlight assembly in relation to the hood (fender) to
obtain correct headlight aim.
accomplished by turning adjusting screw at side of
headlight (Figure 2).
accomplished by turning adjusting screw at top of
headlight (Figure 2).
Fig. 2 Headlight Adjusting Screws
1. Vertical Adjustment
2. Lateral Adjustment
CTS - 4088 Page 3
PRINTED IN UNITED STATES OF AMERICA