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

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

Light, wiper and other major electrical systems

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

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

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

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

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

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

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

Sealed Beam Lamp

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

Halogen Headlamp Bulb Insert Small bulb fits into larger plastic housing

Headlamp Dimmer Switch Controls high and low beam function

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

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

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

Lighting with DRL

Turn Signal, Emergency, and Brake Light Circuits

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

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

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

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

Turn Signal Flasher

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

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

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

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

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

Backup Light Circuit

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

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

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

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

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

Switches

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

Switch Testing A. Connector Removal B. Ohmmeter Check

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

Multifunction Switch Removal B C

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

Exterior Lamp Circuits

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

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

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

Headlight Adjustment Screws Often adjustable without removing the trim

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

Headlight Adjustments

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

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

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

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

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

Instrument Cluster Removal Trim removal Cluster removal

Instrument Cluster Rear-View

Instrument Cluster Disassembly

Dash Gauges

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

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

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

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

Mechanical Speedometer System

Electronic Speedometer System

Electronic Speedometer-Odometer System Speed sensor Speedometer unit Odometer drive

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

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

Heads-Up Display

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

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

Windshield Wiper System Basic parts of a typical system

Windshield Wiper System

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

Windshield Washer System

Wiper Service Refill Blade replacement Arm removal Positioning

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

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

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

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

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

Finding Common Electrical Problems

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

Testing a Fuse

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

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

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

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

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

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

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

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