CH20 lighting systems STUDENT VERSION rev

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Chapter 20

Lighting Systems

• A lamp generates heat and light as current flows through the filament

• Filament vacuum sealed in glass envelope

• Lamps are normally single filament or double filament

Sealed-Beam Headlights

• Air tight assembly

• Contains filament,

reflector, and lens

• Type 1 is high beam

• Type 2 is high and low

beam

Composite Headlights

• Use a replaceable bulb

• Improves aerodynamics, fuel economy, and vehicle styling

HID Headlights

• Also called xenon headlamps

• Use gas-discharge lamps

• Electronically controlled

• Use an electric arc instead of a filament

• Uses high-voltage to jump gap and about 80 volts

to maintain

Headlight Switches

• Controls most exterior lighting

• Instrument panel (IP) lights come on when switch

is in park or headlight position

• IP light brightness may be controlled by rheostat

in headlight switch

• The system can be power-side or ground-side

controlled

Dimmer Switches

• Allows driver to switch between high- and beams

low-• Connected in series with headlight circuit

• Typical dimmer switch

Daytime Running Lights (DRLs)

• Added safety feature

• Headlights connected in series when the ignition switch is on and headlights are off

• When headlights are turned on normal operation returns

Automatic Light Systems

• Light-sensitive, automatic, on-off control

• Uses a photocell sensor/amplifier

• Manual headlight switch operation overrides

Fog Lights

• Designed to send a flat, wide beam under the fog

• Mounted low and aimed low

• Often fitted with yellow or amber lenses to reduce glare

Headlamp Service

• Headlamp failures are usually caused by burned out bulbs

• Check for voltage at the bulb before replacing it

• If more than one lamp is not working, carefully check the circuit

• If the voltage regulator is defective, the high

voltage will cause lamps to burn out prematurely

Headlight Adjustment

• Before adjusting headlights:

– Vehicle must be on a level floor

– Remove ice, snow, or mud

– Try to adjust with fuel tank half full

– Check vehicle ride height

– Inflate tires to specifications

– Wheel alignment should be correct

– Settle the suspension before adjustment

Headlight Adjustment (cont’d)

• Many vehicles have built-in bubble levels for headlight adjustment

• Headlight aiming equipment uses a split mirror system and levels for adjustment

• If neither are available, a screen can be used to determine headlight accuracy

Other Light Bulbs

• Most designs prevent

using incorrect bulb type

• May be several types

within the design

• Bulbs have trade

numbers

Light Circuits

• Single filament bulbs use two wires

• Double filament bulbs will have two hot wires and

a ground

• Light circuits can be either power or ground

controlled

Interior Light Assemblies

• Engine compartment light

• Glove box light

• Luggage compartment light

• Trunk lid light

• Vanity light

Courtesy Lights

• Provides light inside the vehicle

• Operated by doors, headlight switch, or separate switch

• Often tied into keyless entry and/or alarm

• Map lights usually independent of courtesy lights

Rear Exterior Lights

• License plate lights

Turn, Stop, and Hazard Warning Lights

• Each system has a switch to control operation

• Turn signals only powered with key on

• Stop and hazard lights powered with key off

• Turn signal and hazard lights may be part of multifunction switch

• Used by turn signal and hazard systems

• Some styles use temperature sensitive bi-metallic strip

• Many flashers are electronic

• An inoperative turn signal bulb generally causes a different flashing rate

Brake (Stop) Lights

• Controlled by brake light switch normally

mounted on brake pedal bracket

• All late model vehicles have a center

high-mounted stop light (CHMSL)

• Brake light switch input is also used for cruise control, ABS, and traction control systems

Backup Lights

• Operate when transmission is placed in reverse

• May share fuse with turn signal system

• Usually part of transmission range switch on automatic transmissions

• Separate switch on manual transmissions

Basic Lighting System Diagnosis

• Bulbs are quickly checked with ohmmeter or

powered test light

• Inspect for corroded or loose wiring

• Many exterior lights are exposed to climate and weather conditions that can damage wiring and sockets

Bulb Replacement

• Make sure the replacement is the correct bulb

• Inspect the bulb socket

• Often removal of light assembly is necessary

• Do not remove lenses from light assemblies