Lighting Circuits

Today’s technician is required to understand the operation and purpose of the various lighting circuits on the vehicle. The addition of computers and their many sensors and actuators (some that interlink to the lighting circuits) make it impossible for technicians to just bypass part of the circuit and rewire the system to their own standards. If a lighting circuit is not operating properly, the safety of the driver, the passengers, people in other vehicles, and pedestrians are in jeopardy. When today’s technician performs repairs on the lighting systems, the repairs must meet at least two requirements: They must assure vehicle safety and meet all applicable laws.

The lighting circuits of today’s vehicles can consist of more than 50 light bulbs and hundreds of feet of wiring. Incorporated within these circuits are circuit protectors, relays, switches, lamps, and connectors. In addition, more sophisticated lighting systems use computers and sensors. The lighting circuits consist of an array of interior and exterior lights, including headlights, taillights, parking lights, stoplights, marker lights, dash instrument lights, courtesy lights, and so on.

The lighting circuits are largely regulated by federal laws, so the systems are similar between the various manufacturers. However, there are variations. Before attempting to do any repairs on an unfamiliar circuit, the technician should always refer to the manufacturer’s service informations. This chapter provides information about the types of lamps used, describes the headlight circuit, discusses different types of concealed headlight systems, and explores the various exterior and interior light circuits individually.