Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw
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Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

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02.10.2022 Views

Automotive Lighting Systems 269Figure 12-29. Wedge-base bulbs are increasingly used forinterior lighting applications. Historical Fact: Gas LightingHeadlamps that burned acetylene gas were usedon early cars, trucks, and motorcycles.The acetylenegas came from a prefilled pressurized containeror from a “gas generator.”One type of acetylene gas generator used a dripmethod.A tank filled with water was mounted aboveanother tank containing calcium carbide. A valvecontrolled the dripping of water onto the calciumcarbide. When water was allowed to drip onto thecalcium carbide, acetylene gas formed. The gaswas routed through a small pipe to the headlamps.The headlamps were lit with a match or by an electricspark across a special lighting attachment.Wedge-base bulbs generally have been used forinstrument cluster and other interior lighting applications.The base and optical part of the bulb are a onepiece,formed-glass shell with four filament wiresextending through the base and crimped aroundit to form the external contacts (Figure 12-29). Thedesign locates the contacts accurately, permittingdirect electrical contact with the socket, which containsshoulders to hold the bulb in place. The bulbis installed by pushing it straight into its socket,with no indexing required.Wedge-base 2358 bulbs with a new socketdesign were introduced in 1987 as replacementsfor the brass-base 1157 and 2057 bulbs for exteriorlighting applications. The wires of the low-profileplastic socket exit from the side instead of the rear(Figure 12-30). This reduces the possibility of wiredamage and permits the socket to be used in moreFigure 12-30. Wedge-base bulbs with plastic socketsare used for some external lighting applications.(DaimlerChrysler Corporation)confined areas. Since the introduction of this basesocketdesign, a series of these bulbs has beenmade available in both clear and amber versions.TAILLAMP, LICENSEPLATE LAMP, ANDPARKING LAMPCIRCUITSThe taillamps, license plate lamps, and parkinglamps illuminate the car for other drivers to see.Circuit DiagramThese lamps usually share a single circuit becausethe laws of some states require that they be lit at thesame time. Figure 12-31 shows a typical circuitdiagram. Since the main headlamp switch controlsthe lamps, they can be lit whether the ignitionswitch is on or off.

270 Chapter TwelveFigure 12-31.A taillamp, license plate lamp, and parking lamp circuit diagram. (GM Service and Parts Operations)Switches and FusesThese lamps are controlled by contacts within themain headlamp switch. They can be lit when theheadlamps are off (Figure 12-32). A fuse (usually20 amperes) protects the circuit.BulbsThe bulb designs most commonly used as taillampsand parking lamps are the G-6 single-contact bayonetand the S-8 double-contact bayonet. The tail andparking lamps may each be one filament of adouble-filament bulb. License plate lamps are usuallyG-6 single-contact bayonet or T-3 1/4-wedgebulbs.STOP LAMP ANDTURN SIGNALCIRCUITSStop lamps, also called brake lamps, are alwaysred. Federal law requires a red center highmountedstop lamp (CHMSL), on 1986 and laterFigure 12-32. Contacts in the main headlamp switchprovide current to the taillamps, license plate lamps,and parking lamps. (DaimlerChrysler Corporation)

270 Chapter Twelve

Figure 12-31.

A taillamp, license plate lamp, and parking lamp circuit diagram. (GM Service and Parts Operations)

Switches and Fuses

These lamps are controlled by contacts within the

main headlamp switch. They can be lit when the

headlamps are off (Figure 12-32). A fuse (usually

20 amperes) protects the circuit.

Bulbs

The bulb designs most commonly used as taillamps

and parking lamps are the G-6 single-contact bayonet

and the S-8 double-contact bayonet. The tail and

parking lamps may each be one filament of a

double-filament bulb. License plate lamps are usually

G-6 single-contact bayonet or T-3 1/4-wedge

bulbs.

STOP LAMP AND

TURN SIGNAL

CIRCUITS

Stop lamps, also called brake lamps, are always

red. Federal law requires a red center highmounted

stop lamp (CHMSL), on 1986 and later

Figure 12-32. Contacts in the main headlamp switch

provide current to the taillamps, license plate lamps,

and parking lamps. (DaimlerChrysler Corporation)

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