How Do You Wire an Electric Fan Relay Step-by-Step?
When it comes to maintaining or upgrading your vehicle’s cooling system, understanding how to wire an electric fan relay is an essential skill. Whether you’re aiming to improve engine performance, prevent overheating, or simply replace a faulty component, mastering this wiring process can save you time and money. Electric fan relays play a crucial role in controlling the operation of your radiator fan, ensuring it runs only when necessary and protects your engine from excessive heat.
Wiring an electric fan relay might seem intimidating at first, especially if you’re new to automotive electrical systems. However, with a clear grasp of the basics and the right approach, it becomes a straightforward task that even DIY enthusiasts can tackle. This process involves connecting the relay to your vehicle’s power source, fan, and temperature sensor or switch, allowing the fan to activate automatically when the engine reaches a certain temperature.
In the following sections, we will explore the fundamental concepts behind electric fan relays, the tools and materials you’ll need, and step-by-step guidance on how to wire the relay correctly. By the end, you’ll have the confidence to handle this important upgrade or repair, ensuring your vehicle’s cooling system operates efficiently and reliably.
Connecting the Relay to the Fan and Power Source
Begin by identifying the terminals on the relay. Most automotive electric fan relays have four or five terminals, typically labeled as 85, 86, 87, 87a (if present), and 30. Understanding the function of each terminal is crucial for proper wiring:
- Terminal 85: Connects to the ground or chassis of the vehicle.
- Terminal 86: Connects to the control switch or temperature sensor output.
- Terminal 87: Supplies power to the electric fan when the relay is activated.
- Terminal 87a (if present): Provides a normally closed connection, generally unused for electric fan setups.
- Terminal 30: Connects to the battery positive or a fused power source.
To wire the relay correctly, follow these steps:
- Secure a relay socket or prepare connectors compatible with the relay terminals.
- Connect terminal 30 to a fused positive power source, such as the vehicle’s battery through an inline fuse rated appropriately for the fan’s amperage.
- Attach terminal 87 to the positive input wire of the electric fan motor.
- Connect terminal 85 to a solid ground point on the vehicle chassis.
- Link terminal 86 to the fan control signal, typically the output from a temperature switch or the vehicle’s ECU controlling fan operation.
Incorporating a Temperature Switch or Control Signal
The relay coil is energized when the control circuit provides voltage to terminal 86. In electric fan applications, a temperature switch or sensor acts as this control, closing the circuit when the engine coolant reaches a preset temperature. This activates the relay and powers the fan.
When selecting or wiring the temperature switch:
- Ensure the switch rating matches the relay coil voltage, usually 12 volts for automotive systems.
- Position the temperature switch in the coolant system where it accurately senses engine temperature.
- Connect one terminal of the switch to the ignition-switched positive supply (12V only when the engine is running).
- Connect the other terminal of the switch to relay terminal 86.
This setup ensures the fan runs only when necessary, preventing battery drain and extending component life.
Wire Gauge and Fuse Selection
Choosing the correct wire gauge and fuse rating is essential for safety and performance. The electric fan typically draws significant current, so undersized wires or fuses can overheat or fail.
| Fan Motor Current Draw (Amps) | Recommended Wire Gauge (AWG) | Fuse Rating (Amps) |
|---|---|---|
| 0-15 | 14 | 20 |
| 16-30 | 12 | 30 |
| 31-50 | 10 | 50 |
| 51-70 | 8 | 70 |
Key points to consider:
- Use automotive-grade wire with appropriate insulation.
- Install an inline fuse as close as possible to the battery terminal on the positive power feed.
- Ensure the relay is rated to handle the fan’s maximum current load.
Securing and Testing the Wiring
After completing the wiring:
- Double-check all connections for tightness and correct placement.
- Use dielectric grease on terminals to prevent corrosion.
- Secure wires with cable ties and route them away from heat sources or moving parts.
- Test the system by turning the ignition on and allowing the engine to reach the temperature threshold. The relay should click, and the fan should run.
- If the fan does not operate, use a multimeter to verify voltage at relay terminals and continuity through the relay coil.
This methodical approach ensures reliable operation and prevents electrical faults that could damage the fan or vehicle electrical system.
Understanding the Components of an Electric Fan Relay Wiring System
Before wiring an electric fan relay, it is essential to understand the key components involved and their roles within the electrical circuit. This foundational knowledge ensures accurate and safe installation.
- Electric Fan: The device responsible for cooling, usually mounted on the radiator or engine compartment.
- Relay: An electrically operated switch that uses a small current to control a larger current, protecting the control circuit.
- Fuse: A safety device that prevents overcurrent, protecting wiring and components.
- Power Source: Typically the vehicle’s battery or ignition-switched power supply.
- Ground Connection: Completes the electrical circuit and prevents electrical faults.
- Trigger Wire: Usually connected to the temperature sensor or ignition, activates the relay coil.
| Component | Function | Typical Wire Color |
|---|---|---|
| Relay Coil Positive (Trigger) | Receives signal to energize the relay | Blue or Green |
| Relay Coil Ground | Completes coil circuit | Black |
| Power Input to Relay | Supplies battery power to fan when relay is engaged | Red |
| Power Output from Relay | Delivers power from relay to electric fan | Red or Red/White |
| Fan Ground | Completes fan circuit | Black or Brown |
Step-by-Step Guide to Wiring an Electric Fan Relay
The following outlines the precise steps to wire an electric fan relay, ensuring proper functionality and safety.
- Identify Relay Terminals: Most automotive relays have four or five pins, commonly labeled as 85, 86, 30, 87, and sometimes 87a.
- Pin 85: Relay coil ground.
- Pin 86: Relay coil positive (trigger).
- Pin 30: Power input from battery or fuse box.
- Pin 87: Power output to electric fan.
- Pin 87a: Normally closed contact, not used in most electric fan circuits.
- Connect Power Source to Relay Pin 30:
Use an appropriately rated fuse (typically 30-40 amps) inline with the power wire to protect the circuit. Connect this fused wire from the positive terminal of the battery or a switched power source to terminal 30 on the relay. - Connect Relay Pin 87 to Electric Fan Positive:
Run a wire from terminal 87 on the relay to the positive terminal on the electric fan. Ensure the wire gauge is sufficient to handle the fan’s current draw (commonly 14-16 AWG). - Ground the Electric Fan:
Connect the negative terminal of the fan to a clean, chassis ground point or the vehicle’s ground system. This completes the fan’s power circuit. - Wire Relay Coil Ground (Pin 85):
Attach terminal 85 on the relay to a solid ground connection. This ensures the relay coil has a return path. - Connect Relay Coil Positive Trigger (Pin 86):
Connect terminal 86 to the signal source that activates the fan. This can be a temperature switch, a controller output, or ignition-switched power. When this wire receives voltage, it energizes the relay coil, closing the switch between terminals 30 and 87. - Verify All Connections:
Double-check wire routing to avoid heat sources or moving parts. Use proper connectors, such as crimp terminals or solder with heat shrink for durability and corrosion resistance.
Wiring Diagram for Electric Fan Relay
| Relay Terminal | Wire Color | Connection Point | Description |
|---|---|---|---|
| 30 | Red (with inline fuse) | Battery Positive (+) | Power input to relay |
| 87 | Red/White | Electric Fan Positive (+) | Power output to fan |
| 85 | Black | Chassis Ground | Relay coil ground |
