What does the headlight relay do? The headlight relay prevents the headlight switch from overloading and even the vehicle's wiring from burning out in bulbs that consume high current. It ensures that low-power headlights burn more powerfully and prevents light flickering in the headlights. Features: Headlight Relay consists of two independent relays in the same packaging. Headlight Relay constantly provides maximum headlight illumination in the vehicles in which it is used. It minimizes battery consumption by eliminating the need to use H type bulbs. It prevents the failure of long-short flashlight or fog lamp switches, which fail very frequently. It is a relay that you can connect high, low or fog headlights to. Additionally, it is highly resistant to shock, vibration and moisture. As a result of this durability, it operates safely in all climatic and weather conditions. Assembly Diagram.