How An Automotive Relay Works and How to Wire 'Em up

Introduction

Understanding how an automotive relay works is essential for diagnosing and modifying vehicle systems. This tutorial will break down the function of a relay, its components, and how to wire it correctly. By the end, you will have a solid grasp of relay operation and practical wiring techniques.

Step 1: Understand the Relay Components

Before wiring, familiarize yourself with the basic components of a relay:

• Coil: An electromagnetic coil that, when energized, creates a magnetic field.
• Armature: A movable switch that is attracted by the magnetic field created by the coil.
• Contacts: The points where the circuit is made or broken. There are typically two types:
  • Normally Open (NO): The circuit is open until the relay is energized.
  • Normally Closed (NC): The circuit is closed until the relay is energized.

Practical Tip

Always refer to the relay's datasheet for specific pin configurations and ratings.

Step 2: Identify Relay Pin Configuration

Relays usually have a standard pin configuration. For example, a typical 5-pin relay includes:

1. Pin 85: Coil negative
2. Pin 86: Coil positive
3. Pin 30: Common (input)
4. Pin 87: Normally Open (output)
5. Pin 87a: Normally Closed (output)

Common Pitfall

Ensure you correctly identify pins; miswiring can damage the relay or the circuit.

Step 3: Wiring the Relay

To wire a relay, follow these steps:

1. Connect the Coil:

   • Connect Pin 85 to the negative terminal of your power source.
   • Connect Pin 86 to the positive terminal of your power source (this could be a switch or a direct connection).

2. Connect the Load:

   • Connect your load (e.g., a light or motor) to Pin 30.
   • Connect Pin 87 to the positive terminal of the power source for the load.
   • If using NC, connect Pin 87a where needed for your application.

Wiring Example

Here’s a simple example of wiring a relay to control a light:

- Power Source Negative → Relay Pin 85
- Power Source Positive → Switch → Relay Pin 86
- Load (Light) Positive → Relay Pin 87
- Load Negative → Power Source Negative

Step 4: Testing the Relay

After wiring, it’s crucial to test the relay:

1. Verify Connections: Double-check all connections according to the wiring diagram.
2. Power On: Turn on the power source or activate the switch.
3. Check Operation: Ensure the load activates when the relay is energized.

Practical Tip

Use a multimeter to check for continuity at the relay contacts.

Conclusion

In this tutorial, you learned about automotive relays, their components, pin configuration, wiring methods, and testing procedures. Understanding these concepts will enhance your ability to diagnose and modify vehicle systems effectively. For further learning, consider exploring different types of relays and their applications in automotive systems.