Lighting Circuits: Summary

  • The most commonly thought of light circuit is the headlights. But there are many lighting systems in the vehicle.
  • Different types of lamps are used to provide illumination for the systems. The lamp may be either a single-filament bulb that performs a single function, or a double-filament bulb that performs several functions.
  • The headlight lamps can be one of four designs: standard sealed beam, halogen sealed beam, composite, or high-intensity discharge (HID).
  • The headlight filament is located on a reflector that intensifies the light, which is then directed through the lens. The lens is designed to change the circular light pattern into a broad, flat light beam. Placement of the filament in the reflector provides for low- and high-beam light patterns.
  • Some manufacturers use concealed headlights to improve the aerodynamics of the vehicle. The concealed headlight doors can operate from vacuum or by electrically controlled motors. Some systems incorporate the use of IС chips into the concealed headlight door control.
  • In addition to the headlight system, the lighting systems include:
    • Stop lights.
    • Turn signals.
    • Hazard lights.
    • Parking lights.
    • Taillights.
    • Back-up lights.
    • Side marker lights.
    • Courtesy lights.
    • Instrument panel lights.
  • The headlight switch can be used as the control of many of these lighting systems. Most headlight switches have a circuit breaker that is an integral part of the switch. The circuit breaker provides protection of the headlight system without totally disabling the head-light operation if a circuit overload is present.
  • A rheostat is used in conjunction with the headlight switch to control the brightness of the instrument panel illumination lights.