Lighting and Signalling Basics
Lighting circuits, relays and modern headlamp systems.
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What you will learn
- Describe a lighting circuit
- Explain relays and control
- Recognise common lighting faults
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Lighting circuits are textbook switched and protected circuits: a fused supply, a switch or control module, a relay for high current, and a load. Body control modules now control much of the lighting electronically, sometimes over the network.
Faults are usually a bulb, a ground, a relay or the switch/module. Modern LED and matrix headlamps add drivers and calibration, and swapping components can require coding. Poor grounds are a classic cause of dim or flickering lights.
Key points
- Fuse, switch/module, relay, load — follow the circuit.
- Grounds cause dim or intermittent lighting.
- Modern headlamps may need coding/calibration.
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Key points
- Lights are switched and protected circuits
- Relays handle high current
- Modern headlamps need calibration
All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.
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