Car Headlight Wiring Diagram

Hi, in this article, we are going to see the Car Headlight Wiring Diagram and connection with Relays, Batteries, Fusebox, switch, etc. The battery provides the power, while fuses and relays protect the system from electrical overloads. A switch(generally called a Headlight Switch) is located on the dashboard or steering column which allows the driver to turn the headlights on and off or adjust between low and high beams.

High beam and low beam are two modes of car headlights that provide different levels and directions of light to suit various driving conditions. Generally, Dual-filament bulbs are used in the headlight for two different beams - one filament for the high beam and another filament for the low beam. Some vehicles have separate bulbs for high and low beams. When the headlight is operated by the driver, the circuit directs power to the appropriate filament or bulb and it adjusts the beam’s intensity and direction. The low beam is designed to provide a focused and downward-directed light that illuminates the road close to the vehicle. This reduces glare for oncoming traffic, ensuring safe driving in areas with other vehicles. The high beam produces a bright, widespread light that points straight, illuminating a larger area far down the road.

Wiring Diagram

Here you can see the wiring diagram of a car headlight.

Connection Description

• As you can see in the above wiring diagram, two different 4-pin Relays are used for two different Beams.
• The negative terminal of both lights is connected to the chassis ground.
• The High Beam Positive Terminals of both lights are connected to the NO output terminal(87) of the High Beam Relay.
• The Low Beam Positive Terminals of both lights are connected to the NO output terminal(87) of the Low Beam Relay.
• The NO Input terminal of both of the relays is connected to the Positive terminal of the battery through the fuse box.
• The positive terminal of the Coil of both relays is connected to the positive terminal of the battery or the Ignition Key through the Fuse Box.
• The negative terminals of both relay coils are connected to the chassis ground through the Headlight Switch.

Operation Principle

The car headlight wiring works by using two 4-pin relays, one for the high beam and one for the low beam. 

When the driver turns on the headlight switch, it connects the relay coil to the ground and activates the relay. This allows electricity to flow from the battery, through the fuse box, to the correct beam (high or low). 

The high beam relay powers the high beam lights, and the low beam relay powers the low beam lights. Both relays ensure that the lights get power only when needed. 

The negative terminals of the lights are connected to the car's chassis to complete the circuit. 

The fuse box protects the system from any electrical overloads, and the ignition connection ensures the lights work only when the car is on.

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