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The headlight main beam relay is an electrically operated switch and is used in a vehicle’s wiring to minimise voltage loss from the battery to the headlights. In basic headlight wiring systems, the power will travel from the battery to the headlight switch and then finally to the headlights. When a model> headlight main beam relay is fitted, the voltage goes from the battery to the relay and then directly to the headlights to control the main beam. Because the power has a shorter distance to go, the voltage loss is smaller meaning that the headlights perform better and put out more light. It’s also possible to add higher output bulbs without overloading your headlight wiring.
The headlight main beam relay also protects the switch from overheating from high amperage. Most vehicles use two relays to control the flow of power successfully, one for the high beam and one for the low beam wiring.
Relays can fail because of oxidisation, overheating or due to a faulty connection in the relay socket. If the headlight main beam relay shows signs of failure your headlights may become dim. This can eventually lead to headlight failure.