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Lighting and Wiring Service
Chapter 33
© 2012 Delmar, Cengage Learning
Objectives
• Diagnose problems in lighting and wiring
systems
• Adjust headlamp aim
• Make repairs to automotive wiring, lamps and
bulbs, and protection devices
© 2012 Delmar, Cengage Learning
Analyzing Electrical Problems
• Diagnose problem cause
– Verify the complaint
– Check for related symptoms
– Check wiring diagram for common problems
• Problem types
– Open circuit: break in continuity
– Short circuit: unwanted current path
• Grounded circuit: short circuit to ground
– Excessive resistance: reduces current flow
• Corroded connector is a common cause
© 2012 Delmar, Cengage Learning
Wiring Service
• Wiring diagrams: road maps to electrical circuits
– Wires are numbered or colored
• First color is insulation; second is stripe
• Numbers refer to wire gauge or locations
– Letters preceding the number
• G: grounds
• S: splices
• C: connectors
– SAE wiring diagrams
• Arranged so upper right is power feed
• Lower right is ground
© 2012 Delmar, Cengage Learning
Crimp Terminals
• Install terminal on wire
– Strip about ¼ inch of insulation from end of wire
– Insert wire end into terminal and crimp
• Poor crimp creates excessive resistance
• W-crimp crimps longitudinally
• Terminal block keeps wires organized
– Depress locking tang to remove terminals
• Crimp connectors splice wires together
– Insert both ends into connector and then crimp
– Wires should be side by side
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
Selecting Replacement Wire
• Replacement wire and cable
– Comes wound in spools
– Use wire adequate for load
– Replacement wire should be at least as big as
original
– Wire that is too small or too long causes
excessive resistance
– Doubling the length doubles the resistance
© 2012 Delmar, Cengage Learning
Adding Electrical Accessories
• Aftermarket accessories
– Usually require separate fused circuit
• Fuse holders
– Original equipment accessories take power from
a fuse on the fuse panel
• Fuse holder can be connected to existing power
source
• Tap splice connectors are used in electrical
circuits only, not in electronic circuits
© 2012 Delmar, Cengage Learning
Soldering
• Preferred for electronic circuits
– Small amount of current runs through
– Does not suffer increased resistance due to
oxidation
• Soldering iron is used for wiring connections
– Propane, acetylene, Mapp gas torch are used for
radiators or larger cable terminal connections
• Stainless steel is not solderable
• Flux cleans metal so solder will stick
© 2012 Delmar, Cengage Learning
Soldering (cont'd.)
• Cold solder connection
– Solder melts but wire does not bond to it
• Heat-shrink tubing
– Insulates a solder joint and makes it airtight
• Connection can also be insulated with vinyl tape
• Adhesive-lined tubing
– Recommended to prevent corrosion
© 2012 Delmar, Cengage Learning
Broken or Damaged Ground
Straps
• Engine and body: isolated from frame with
rubber mounts
– Ground straps between engine and chassis
provide path back to battery through frame
• Broken ground strap may cause:
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Burned transmission bushing and drive shaft yolk
Burned emergency brake cables
Burned carburetor return spring
Flickering headlights
Burned front-wheel bearings or CV joints
© 2012 Delmar, Cengage Learning
Circuit Testing and Service
• Fuse failure
– Replaced fuse does not fix the problem that
caused the overload
• Fix the problem before restoring circuit protection
– Corrosion at fuse end can cause failure
• Fuses are rated according to current capacity
– Not voltage
• Fuses have 10% overload factor
– Guards against minor power surges
© 2012 Delmar, Cengage Learning
Finding Grounds
• Locating the cause of a grounded wire
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Install a circuit breaker temporarily
Install a test light in series with the circuit breaker
Disconnect individual circuits
Circuit disconnected when light goes out is at
fault
• Compass or Gauss meter
– Locates ground location
• Ohmmeter
– Detects grounded circuit
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
Fuse Testing and Service
• Checking fuses
– Visual check, ohmmeter, and test light
• Removing fuses
– Blade-type: removed by hand or with pliers
• Test light does not glow on either circuit side
– Circuit is shut off
– Circuit is broken
– Tester does not have good ground connection
• Be sure replacement fuse has correct rating
© 2012 Delmar, Cengage Learning
Fuse Link Service
• Fuse link
– Length of wire covered with insulation that is
thicker than normal insulation
• Can contain melted metal if a wire fails
– Insulation bubbles if fuse link melts
• Cut out damaged part of wire
• Splice new fuse link
• Use a fuse link of the correct size
© 2012 Delmar, Cengage Learning
Headlamp Service
• Headlight: light beam from a headlamp
• Replacing a headlamp
– Halogen and conventional sealed beams will fit
into same brackets
– Round type I and type II lamps do not
interchange
– Use dielectric grease when installing headlight
• Halogen lamp replacement
– Sealed-beam halogen lamps: replaced as a unit
© 2012 Delmar, Cengage Learning
Headlamp Service (cont’d.)
• Composite halogen lamp insert replacement
– Removing a halogen replaceable lamp insert in a
composite light assembly
• Touch it only on its plastic base
• HID lamp service
– High-intensity discharge (HID) lamps
• Expensive but reliable
• Two to three times less likely to fail
© 2012 Delmar, Cengage Learning
Headlight Aiming
• Properly aimed low-beams: face down and right
• Before adjusting headlights check that the:
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Vehicle is carrying its typical load
Trunk is carrying typical amount of material
Gas tank is half-full
Driver’s weight is accounted for
• Headlight-mounted aimers
– Use bubble levels to calibrate vertical alignment
– Horizontal alignment compares headlights to see
they are parallel
© 2012 Delmar, Cengage Learning
Headlight Aiming (cont'd.)
• Electronic optical aimers
– Laser technology is used to square and align
• Locating the optical center of the headlight
– Electronic optical headlight aimer slides on track
• Aimer alignment to headlight
– Align the aimer to the headlight
• Lamp audit and aim
– Follow arrow indicator
• More precise aiming
– Use “Aim Lamp” button
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
Tail Lamp and Park Light
Service
• Lamps may be accessed from inside the trunk
– Others require removal of light lens
• Excessive voltage
– Shortens the life of a light bulb
• Voltage higher by five percent reduces bulb life by
half
– Malfunctioning charging system is the only cause
of excessive voltage
© 2012 Delmar, Cengage Learning
LED Service
• Light-emitting diodes (LEDs)
– Sometimes used for headlights, brake lights, turn
signals, and taillights
– Also used in side rear view mirror turn signal
indicators and center high-mount stop lamps
– Not serviceable; they are replaced
– Use less current than filament light bulbs
© 2012 Delmar, Cengage Learning
Stoplight Switch Service
• Bypass stoplight switch with jumper wire to test
– Stoplights should light when wires are connected
• Use a test light to see if there is power at one
end
– If lights come on when wires connected, but not
when brakes are applied, replace the switch
– If lights stoplights operate without key, remove
the fuse before removing switch
– If new switch adjustable, adjust it so it is open
when the pedal is released
© 2012 Delmar, Cengage Learning
Back-Up Lights
• Back-up light circuit components
– Fuse
– Shift lever or transmission mounted switch
• Sometimes adjustable
– Wiring
– Lights
• Back-up lights could come on in a gear range
other than reverse
– Check the service information for adjustment
procedures
© 2012 Delmar, Cengage Learning
Turn Signal Switch
• Defective switch
– May not cancel signal following sharp turn
– Brake light problems may be caused by defective
signal switch
• Multifunction switch removal
– Most newer passenger vehicles use a
multifunction switch
• Includes turn signal switch
• Can often be removed without removing steering
wheel
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Signal Flasher/Relay
• Electronic signal flashers
– Flash faster than normal when bulb has failed
• Mechanical flashers flash slower
– Turn on hazards and walk around the car to
check filaments of signal bulbs and break lights
© 2012 Delmar, Cengage Learning
Locating a Signal Flasher
• Several flasher locations
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In the fuse panel
Under the dash in a wiring loom
In glove box
Under the hood
• Location flashers
– Most are located under dashboard on driver’s
side
– Working: can be located by clicking sound
– Not working: use service information
© 2012 Delmar, Cengage Learning
Instrument Panel Bulbs and
Windshield Washer Service
• Small bulbs resembling photo flash bulbs
– Printed circuit dash boards
• Housed in plastic connector
• Turn ¼ turn counterclockwise to remove
• Primary reason for windshield washer problems
– Restriction in washer nozzle
• Pull one of the hoses off a nozzle and operate
washer
• Fluid is pumped from end of hose: clean nozzle
• No fluid pumped: check fuse
• Problem is with pump: replace it
© 2012 Delmar, Cengage Learning
Horn Service and Gauge
Testing
• Horn does not work: check fuse
– Horn can adjusted by changing the spring
tension on the armature
• When a gauge does not operate: check its fuse
– Fuse in tact, but no power: check wiring diagram
– Work toward battery checking voltage
• Sending unit tests
– Use an ohmmeter to check resistance between
the terminal of the sending unit and ground
© 2012 Delmar, Cengage Learning