Install A Standard 4 Pin Relay For The Front Lights Of A Car

Most vehicles use standard four-pin relays to regulate power to the front headlights. When the headlight switch is on, the headlight relay‘s internal circuitry completes the circuit, allowing power to flow to the lights. When the headlight relay fails, the headlights operate intermittently or fail to operate. Replacement light relays are available from auto parts stores and new car dealerships.


1. Place the vehicle’s transmission into first gear (standard transmission) or park (automatic transmission). Turn off the engine.

2. Open the hood and locate the under-hood relay control box. It is generally on the right or left side of the vehicle, depending upon the make and model. It is a square box with a black plastic cover.

3. Remove the cover from the box by depressing the plastic locking tabs and lifting off the cover. Read the diagram imprinted on the underside of the cover to locate the front light relay within the relay control box.

4. Grip the relay between your thumb and index finger and pull it straight out. Install the new relay in its place and replace the relay box cover. Test the front lights to ensure they work properly.

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