4-Pin Relay: Functions, Applications, and Wiring Guide

 A 4-pin relay is an essential component in automotive electrical systems, used for switching high-power circuits with a low-power signal. It helps control lights, fans, fuel pumps, and other vehicle accessories efficiently.

Functions of a 4-Pin Relay
 1. Control High-Power Circuits – Allows a small current to switch a larger current.
 2. Protects Electrical Systems – Prevents switches from handling high amperage, reducing wear.
 3. Enhances Safety – Ensures stable operation of automotive components.

Applications of a 4-Pin Relay
 • Headlights and fog lights
 • Electric cooling fans
 • Horns and alarms
 • Fuel and ignition systems

Wiring Guide for a 4-Pin Relay

A 4-pin relay consists of:
 • Pin 30 (Common): Connected to the power source.
 • Pin 87 (Normally Open - NO): Connects to the load (e.g., a fan or light).
 • Pin 85 (Coil Ground): Connects to the ground.
 • Pin 86 (Coil Power): Connects to the switch or control circuit.

Wiring Steps:
 1. Connect Pin 30 to the battery (with a fuse for protection).
 2. Connect Pin 87 to the positive terminal of the load.
 3. Connect Pin 85 to the ground.
 4. Connect Pin 86 to a switch, which gets activated by a control signal.

By understanding and correctly wiring a 4-pin relay, you ensure the safe and efficient operation of automotive electrical systems.