1. Lights, Instrumentation,
Chapter 37
Lights, Instrumentation,
Wipers, and Horns-
Operation and Service

2. Contents Lighting systems Light system service Instrumentation
Windshield wipers
Horns
Finding common electrical problems

3. Light, wiper and other major electrical systems

4. Lighting Systems Operate the interior and exterior lights Components:
fuses
wires
switches
relays

5. Light switch feeds current to the circuits
Lighting Systems
Light switch feeds current to the circuits

6. Headlamp System Components: battery headlamp wiring fuse panel
light switch
dimmer switch
headlamps, taillights, marker lights and instrument lights

7. Controls current to the headlamp system
Headlamp Switch
Controls current to the headlamp system

8. Multifunction Switch Controls several circuits
headlights (high and low beams)
flash-to-pass (energizes high beams)
turn signals
cruise control
windshield wipers

9. To test, probe voltage in different switch positions
Multifunction Switch
To test, probe voltage in different switch positions

10. Headlamp Bulbs One or two filaments in a vacuum-sealed glass housing
Filament gets white-hot and glows
Reflector and lens direct this light forward

11. Sealed Beam Lamp

12. Halogen Headlamp Bulb Insert
Made of heat-resistant quartz filled with halogen gas to protect the filament
About 25% brighter
Typical low beam–45 watts
Typical high beam–65 watts
Maximum low beam brightness–20,000 candle power

13. Halogen Headlamp Bulb Insert
Small bulb fits into larger plastic housing

14. Headlamp Dimmer Switch
Controls high and low beam function

15. Automatic Headlamp System
Uses a light sensor, amplifier and relay to control high and low beams
Automatically dims the lights when detecting light from oncoming traffic
Switches to high beam with no oncoming light

16. Operation
Light sensor or photosensor in the grill or on the dash, produces current when exposed to light
Amplifier uses this current to operate a dimmer relay
Relay changes from high to low beam
Some turn the headlamps on when dark, others turn the headlamps off after a short delay period

17. Daytime Running Lights (DRL)
Headlamps are lit anytime the engine is running
This lighting system makes the vehicle more visible

18. Lighting with DRL

19. Turn Signal, Emergency, and Brake Light Circuits

20. Common Bulbs Used in backup and marker lights
Used in parking, turning, and brake lights

21. Turn Signal System Components: fuse turn signal switch flasher unit
turn signal bulbs
indicator bulbs
related wiring

22. Mounted around the steering shaft
Turn Signal Switch
Mounted around the steering shaft

23. Turn Signal Flasher
Automatically opens and closes the turn signal circuit, causing lamps to flash
Contains a temperature-sensitive bimetallic strip and heating element
When current flows through the flasher, the bimetallic strip is heated and bends
This opens points, opening circuit
Strip rapidly cools, closing circuit

24. Turn Signal Flasher

25. Emergency Lights Hazard lights Components:
switch
flasher
turn signal lamps
related wiring
When the switch is closed, current flows through the emergency flasher, causing all turn signals to flash

26. Brake Light System Components: fuse brake light switch rear lamps
related wiring

27. Operation Battery power is fed to the brake light switch
When the brake pedal is pressed, it closes the switch, current flows to the brake lights
Switch may be located on master cylinder, closed by hydraulic pressure

28. Brake Pedal Switch Pedal released, contacts open
Pedal depressed, contacts closed

29. Backup Light System Components:
fuse
gear shift or transmission-mounted switch
two backup lamps
wiring
Illuminates area behind the car when transmission is shifted into reverse

30. Backup Light Circuit

31. Illuminated Entry System
Turns on the interior lights when you move the door handle or open the door

32. Light System Service Light system service involves:
changing burned-out bulbs
testing bulb sockets
checking fuses
finding shorted and open circuits
aiming headlights

33. Headlamp, turn signal, and side marker light assemblies
Lamp Replacement
Headlamp, turn signal, and side marker light assemblies

34. Bulb Configurations A. Partial turn B. Push in and turn
C. Push in D. Double-end

35. Oil on your skin can make the bulb shatter
Bulb Replacement
Oil on your skin can make the bulb shatter

36. Switches

37. Light Switch Problems Switch may become shorted or open
If shorted closed, lights will always glow
If always open, lights will not work
To test, use a test light or voltmeter
Check for power going to and from the switch
Disconnect switch and check resistance with an ohmmeter

38. Switch Testing
A. Connector Removal
B. Ohmmeter Check

39. Turn Signal Problems If one side will not flash, check bulbs
Even one burned bulb will reduce current and prevent flasher from working
If both sides do not work, check fuse and flasher unit
Multifunction switch may wear and malfunction

40. Multifunction Switch RemovalB C

41. Brake Light Problem
If none of the lights are working, something common to all bulbs is at fault–brake light switch or feed circuit
If one bulb is not working, the bulb and its section of the circuit should be checked

42. Exterior Lamp Circuits

43. Aiming Headlights Aiming methods:
mechanical aimers
wall screen
leveling bubbles on headlamp housing
Aim with half tank of gas, correct tire inflation, spare tire and jack in the trunk

44. Headlight Aimers
Leveling bubbles show vertical adjustment, mirror reflection shows horizontal adjustment

45. Headlight Aiming Screen
Adjust low beams until they shine in designated areas on the wall

46. Headlight Adjustment Screws
Often adjustable without removing the trim

47. Leveling bubble provided for adjustment
Headlight Assembly
Leveling bubble provided for adjustment
Adjusting screw
Leveling bubble

48. Headlight Adjustments

49. Instrumentation Informs driver of various operating conditions
oil pressure
engine temperature
computer trouble codes
air bag system status

50. Rotating needles or dials indicate operating conditions
Analog Instruments
Rotating needles or dials indicate operating conditions

51. Lights and electronic displays show operating conditions
Digital Instruments
Lights and electronic displays show operating conditions

52. Vacuum Fluorescent Displays
VFD
Small glass tubes filled with neon or argon gas
Segments glow when electrically energized
Very visible and easy to read

53. Liquid Crystal Displays
LCD
Semiconductor panels pass light when electrically energized
Panels block light when not energized
Often backlighted with a bulb

54. Instrument Cluster Removal
Trim removal
Cluster removal

55. Instrument Cluster Rear-View

56. Instrument Cluster Disassembly

57. Dash Gauges

58. Dash Gauges Balancing coil gauge
Two electric coils cause needle deflection
Sending unit changes current flow through the coils changing magnetic fields, deflecting needle
Two coil windings magnetically attract the needle

59. Dash Gauges Bimetal gauge
Two dissimilar metals bonded together cause gauge needle deflection
As current flow from sending unit increases, bimetal strip heats and deflects more
Less current flow causes less bending, less needle movement
Thermostatic strip moves the needle

60. Sending Units Control current flow through the gauges
Constructed from variable resistors
Types:
oil pressure
fuel level

61. Speedometers Mechanical speedometer components:
drive gears
cable
mechanical head
Electronic speedometer components:
vehicle speed sensor
electronic control module
electronic display

62. Mechanical Speedometer System

63. Electronic Speedometer System

64. Electronic Speedometer-Odometer System
Speed sensor
Speedometer unit
Odometer drive

65. Driver Information Center
Dash mounted keyboard-display for inputting and reading data
Information available:
miles-to-empty
average fuel consumption
estimated time of arrival

66. Heads-Up Display
Reflects display information onto the windshield or plastic dash panel for easy viewing while driving
Driver can see the road while reading data

67. Heads-Up Display

68. Heads-Up Display LED at A is reflected to B
Driver sees virtual image at C

69. Windshield Wipers Components: switch motor assembly
wiper linkage and arms
wiper blades
washer system

70. Windshield Wiper System
Basic parts of a typical system

71. Windshield Wiper System

72. Plastic gears may be replaceable
Wiper Motor Assembly
Plastic gears may be replaceable

73. Windshield Washer System

74. Wiper Service
Refill
Blade replacement
Arm removal
Positioning

75. Rain-Sensing Wipers
Automatically turns the wipers on when water is detected on the windshield
Light-emitting diode and a light sensor detect water
Electronic control module can turn on wipers

76. Rain-Sensing Wipers A. Sensor and ECM B. Windshield clear, wiper off
Windshield wet, wiper on

77. Horns Components: When horn switch is closed, it activates horn relay
fuse
horn switch
horn
wiring
When horn switch is closed, it activates horn relay
Relay carries high horn current

78. Horn Contains coil, points and flexible diaphragm
Coil and point action makes plunger slide in and out of coil, moving diaphragm

79. Horn may have adjustment screw to set current flow
Horn Adjustment
Horn may have adjustment screw to set current flow

80. Finding Common
Electrical Problems

81. Short Circuit Short to power Short to ground (unintentional ground)
Current-carrying wire is touching another wire or ground
May cause blown fuse, burned fusible link or open circuit breaker
A short to another wire may cause the wrong system to operate

82. Testing a Fuse

83. Test for Short Circuit
Connect a test light across fuse terminals (fuse removed)
If a short to ground is present, light will glow
Disconnect related circuit components until light goes out
When light goes out, you have removed short to ground

84. When light goes out, shorted circuit has been disconnected
Test for Short Circuit
When light goes out, shorted circuit has been disconnected

85. Always use a fuse with the same rating
Fuse Replacement
Always use a fuse with the same rating

86. Open Circuit Prevents systems from working
Caused by broken wire, disconnected electrical connection or switch
To test, use a test light or voltmeter
Check for power at the supply (fuse), moving toward the component (load) if power is found

87. High Circuit Resistance
Reduces current flow in a circuit
Motors may run slow, lights may be dim
To test, measure voltage drop across suspected problem components such as a switch
High resistance causes high voltage drop
Maximum 0.5 volts for a feed circuit

88. Using Wiring Diagrams
Diagrams show the relationship of wires and components
Information available:
wire color coding
component location
splices and connections
symbols
component drawings

89. Relay Problems Worn, burned or sticking contact points
Coil windings can break, preventing point closure
To test, use a test light or voltmeter
Verify voltage signal and ground at the windings
Check for voltage at output terminal with contact points closed

90. Relay
Sometimes, you can remove an identical relay from another system and substitute for a quick test