SERVICE MANUAL INTRODUCTION 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 repairs. 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 circuit diagram. HEADLIGHTS HEADLIGHT AIMING Various types of headlight aiming equipment are available  commercially.    When  using  aiming  equipment, follow instructions provided by the equipment manufacturer. Where     headlight     aiming equipment is not 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 the chart. Fig. 1 Headlight Aiming Pattern 1. Projected Beam 5. Right Light Center Height 6. Projected Beam 2. Left Light Pattern (Upper Beam) 3. Center of Truck 7. Floor Line 4. Headlamp Center Height 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 ADJUSTMENT). IMPORTANT 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. HEADLIGHT ADJUSTMENT Adjusting    screws    are    provided    to    move    the headlight  assembly  in  relation  to  the  hood  (fender)  to obtain correct headlight aim. Lateral or side-to-side adjustment is accomplished   by   turning   adjusting   screw   at   side   of headlight (Figure 2). Vertical or up-and-down adjustment is 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