The 4 Pin Automotive Relay is a fundamental component in modern vehicles, responsible for controlling high-current circuits with a low-current signal. This guide delves into the intricacies of this small but powerful device, covering its functionality, types, wiring diagrams, and common applications.
What is a 4 Pin Relay?
A relay is essentially an electrically operated switch. The 4 pin relay, specifically, is a type of electro-mechanical relay commonly found in automotive applications. It utilizes a low-current signal to activate an electromagnet, which in turn closes a high-current circuit. This allows a small switch or a low-current electronic component to control a device that draws significant amperage, like headlights, fans, or fuel pumps. This isolates sensitive components from high current loads and prevents damage.
How a 4 Pin Relay Works
Inside the relay, you’ll find an electromagnetic coil, an armature, and a set of contacts. When a small current is applied to the coil (terminals 85 and 86), it generates a magnetic field. This field attracts the armature, which physically moves a contact, closing the high-current circuit (terminals 30 and 87). When the current to the coil is removed, the magnetic field collapses, the armature returns to its original position, and the high-current circuit opens.
Internal components of a typical automotive relay.
Terminal Identification: Decoding the Numbers
Each of the four pins on the relay has a specific function and corresponding number:
- 85: Coil Ground – This pin connects to the ground or negative side of the control circuit.
- 86: Coil Power – This pin connects to the positive side of the control circuit, providing the low-current signal to activate the relay.
- 30: Common – This pin is the input for the high-current circuit, often connected directly to the battery or a fused power source.
- 87: Normally Open (NO) – This pin is the output for the high-current circuit. When the relay is activated, this terminal connects to terminal 30, completing the circuit.
Standard pin numbering on a 4 and 5 pin automotive relay.
Common Applications of 4 Pin Relays
4 pin relays are used extensively in various automotive systems, including:
- Headlight Control: Activating high-beam headlights, drawing power directly from the battery while using the headlight switch as the low-current trigger.
- Cooling Fan Operation: Turning on electric cooling fans when the engine reaches a certain temperature, utilizing a temperature sensor as the trigger.
- Fuel Pump Control: Energizing the fuel pump when the ignition is switched on.
- Horn Activation: Using the relatively low current horn switch to trigger the relay and power the higher current horn.
- Starting System: Engaging the starter motor using the ignition switch as a trigger.
Wiring Diagram Examples: Practical Implementations
Here are two examples illustrating typical 4 pin relay wiring scenarios:
Example 1: Driving Lights Controlled by High Beams
Wiring diagram for driving lights triggered by the high beam circuit.
In this setup, the high beam signal provides the low-current trigger to activate the relay, powering the driving lights only when the high beams are on.
Example 2: Headlight-On Warning Buzzer
Wiring a warning buzzer to sound when headlights are left on.
This circuit utilizes the headlight power and the door switch to activate a buzzer if the headlights are left on when the door is opened.
Choosing the Right Relay
When selecting a 4 pin relay, consider the following factors:
- Voltage Rating: Ensure the relay’s voltage rating matches your vehicle’s electrical system (typically 12V).
- Current Rating: Choose a relay with a current rating that exceeds the maximum current draw of the device it will control.
- Terminal Type: Confirm the terminal type matches your wiring connectors.
Conclusion: The Unsung Hero of Automotive Electrical Systems
The 4 pin automotive relay is a critical component, enabling efficient and safe control of high-current circuits throughout your vehicle. Understanding its operation and applications empowers you to diagnose potential issues and perform necessary modifications or repairs. By leveraging the power of the relay, automotive engineers ensure reliable performance and extended lifespan of various electrical systems.
