10. Figure 42–1 Bulbs that have the same trade number have the same operating voltage and wattage. The NA means that the bulb uses a natural amber glass ampoule with clear turn signal lenses. Continued
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12. Figure 42–2 This single-filament bulb is being tested with a digital multimeter set to read resistance in ohms. The reading of 1.3 ohms is the resistance of the bulb when cold. As soon as current flows through the filament, the resistance increases about 10 times. It is the initial surge of current flowing through the filament when the bulb is cool that causes many bulbs to fail in cold weather as a result of the reduced resistance. As the temperature increases, the resistance increases. Continued
13. Figure 42–3 Close-up a dual-filament (double-filament) bulb (#1157) that failed. Notice that one filament (top) broke from its mounting and melted onto the lower filament. This bulb caused the dash lights to come on whenever the brakes were applied. Continued
14. Figure 42–4 Bulbs #1157 or #2057 are typically used for taillight and front parking lights. These bulbs contain both a low-intensity filament for taillights or parking lights and a high-intensity filament for brake lights and turn signals.
17. Figure 42–5 Corrosion caused the two terminals of this dual-filament bulb to be electrically connected. Figure 42–6 Often the best diagnosis is a thorough visual Inspection. This bulb was found to be filled with water, which caused weird problems.
18. Many automotive bulbs have the same operating parameters (same wattage, voltage, amperage, and candlepower) yet have different trade numbers. Some numbers are for standard duty, others have heavier filament wire or additional filament support, which qualifies them for a different trade number. Fleet-duty designation represents a durability increase; heavy-duty designation identifies the most severe service bulb. Heavy-Duty Automotive Bulbs Therefore, if the specification for your vehicle gives a trade number under the “regular” heading, you can safely switch to a bulb listed under the “fleet-duty” or “heavy-duty” heading. For best operation of turn signals and consistent brightness of bulbs, the switch of trade numbers should include all similar bulbs of the type being replaced. See the bulb equivalence chart on Page 462 of your textbook.
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20. A common cause of an inoperative cruise control, especially on General Motors vehicles, is a burned out bulb in the third stop light. The cruise control uses the filaments of the third brake bulb (CHMSL) as a ground and shuts off the cruise if the bulbs are burned out (open). See Fig. 42-7. No Cruise Control? Check the Third Brake Light
21. Figure 42–7 Typical brake light and taillight circuit showing the brake switch and all of the related circuit components. See the schematicon Page 463 of your textbook.
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25. Figure 42–9 To remove the headlight switch from a vehicle that uses a knob and shaft, a release button has to be pushed to release the shaft. After the knob and shaft assembly has been removed, then the retaining nut can be removed from the headlight switch so it can be removed from the dash.
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29. Figure 42–12 Typical headlight-aiming diagram as found in a service manual. See the diagramon Page 465 of your textbook.
30. Figure 42–13 Many composite headlights have a built- in bubble level to make aiming easy and accurate.
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46. Figure 42–20 Typical dash-mounted switch that allows the driver to disable the adaptive front lighting system.
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48. Figure 42–21 Typical daytime running light (DRL) circuit. Follow the arrows from the DRL module through both headlights. Notice that the left and right headlights are connected in series, resulting in increased resistance, less current flow, and dimmer than normal lighting. When the normal headlights are turned on, both headlights receive full battery voltage, with the left headlight grounding through the DRL module.
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55. Figure 42–25 When stop lamps and turn signals share a common bulb filament, stop light current flows through the turn signal switch. Continued
56. Figure 42–26 When a right turn in signaled, the turn signal switch contacts send flasher current to the right-hand filament and brake switch current to the left-hand filament.
57. Light-emitting diode ( LED ) brake lights are frequently used for high-mounted stop lamps (CHMSL) for several reasons including : Why are LEDs Used for Brake Lights? Faster illumination. An LED will light up to 200 milliseconds faster than an incandescent bulb, which requires time to heat the filament before it is hot enough to create light. This faster illumination can mean the difference in stopping distances at 60 mph (100 km/h) by about 18 feet (6 meters) due to the reduced reaction time for the driver of the vehicle behind. Longer service life. LEDs are solid-state devices that do not use a filament to create light. As a result, they are less susceptible to vibration and will often last the life of the vehicle. Aftermarket replacement LED bulbs that are used to replace conventional bulbs may require the use of a different type of flasher unit due to the reduced current draw of the LED bulbs. See Figure 42–27.
58. Figure 42–27 A replacement LED taillight bulb is constructed of many small individual light-emitting diodes. NOTE: Some vehicles are equipped with outside mirrors that include an LED arrow that flashes with the turn signal. These LEDs are not service-able separately, but are serviced with the mirror as an assembly.
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70. A question that service technicians are asked frequently is why the side marker light alternately goes out when the turn signal is on and is on when the turn signal is off. Some vehicle owners think that there is a fault with their vehicle while actually it is normal operation. The side-marker light goes out whenever the lights are on and the turn signal is flashing because there are 12 volts on both sides of the bulb (see points X and Y in Figure 42–30). Normally, the side-marker light gets its ground through the turn signal bulb. Why Does the Side-Marker Light Alternately Flash?
71. Figure 42–30 The side-marker light goes out whenever there is voltage at both point Xand Y. These opposing voltages stop current flow through the side-market light. The left turn light and left park light are actually the same bulb (usually a #2057) and are shown separately to help explain how the side-marker light works on many vehicles.
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74. The switches in the doorjamb simply signal the computer that a door has been opened. The computer controls lighting to help prevent accidental battery drain. For example, if the vehicle door has been left open, the computer can open the circuit and prevent a dead battery. The schematic rarely shows exactly how the circuit works. However, the service information walks you through the diagnosis. With a service manual, or computerized information service, the technician is never lost. Always follow the procedures exactly! Even if the service procedure sounds long and involved, the procedure will lead you to the correct diagnosis. Service Manual Diagnosis
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