Embarking on automotive projects or troubleshooting electrical issues can feel daunting, but understanding the core components is key. At the heart of many electrical systems lies the humble yet powerful relay. Specifically, a well-understood 87 relay wiring diagram is crucial for anyone looking to harness the power of these switching devices. This guide will demystify the 87 relay wiring diagram, explaining its purpose and how it functions to simplify complex electrical circuits.
What is an 87 Relay Wiring Diagram and How is it Used?
An 87 relay wiring diagram is essentially a blueprint for a specific type of automotive relay, often referred to as a "SPDT" (Single Pole, Double Throw) or "changeover" relay. These relays act as electrically operated switches. They use a low-current circuit to control a high-current circuit, effectively allowing a small amount of power to manage a much larger load. The "87" in the context of an 87 relay wiring diagram typically refers to the terminal number on the relay that connects to the normally open contact. This is a critical distinction that differentiates it from other relay types.
The primary function of an 87 relay wiring diagram is to illustrate how to connect the relay's terminals to achieve the desired switching action. These diagrams are indispensable for several reasons:
- Simplifying Power Distribution: They allow for the safe and efficient control of high-draw components like headlights, fuel pumps, horns, and starter motors.
- Protecting Switches: By using a relay, the actual switch (like a dashboard button) only handles the small current needed to energize the relay coil, preventing it from burning out.
- Creating Complex Circuits: They enable the creation of circuits where one switch can control multiple devices, or where devices only operate under specific conditions (e.g., headlights only turning on with the ignition).
The basic operation involves four or five pins on the relay. When interpreting an 87 relay wiring diagram, you'll typically see the following connections:
| Terminal Number | Function | Description |
|---|---|---|
| 30 | Common | The input from the power source. |
| 85 | Coil Negative | Connects to ground or negative battery terminal. |
| 86 | Coil Positive | Connects to the control switch (e.g., dashboard button). |
| 87 | Normally Open (NO) | Connects to the load when the relay is energized. This is the terminal we are focusing on in an "87 relay wiring diagram." |
| 87a (Optional) | Normally Closed (NC) | Connects to the load when the relay is NOT energized. |
When current flows through terminals 85 and 86, it energizes the relay's coil. This magnetic field pulls an internal contact, disconnecting terminal 30 from 87a (if present) and connecting it to terminal 87. This allows the high-current circuit to be completed. The ability to control high-power devices with a low-power signal is the most important aspect of using an 87 relay wiring diagram effectively.
To further illustrate, consider a common application: activating fog lights. An 87 relay wiring diagram for this setup would show the vehicle's battery (positive) connected to terminal 30. Terminal 86 would connect to a fog light switch on the dashboard, and terminal 85 would connect to ground. The fog lights themselves would be connected to terminal 87. When the fog light switch is pressed, power flows to terminal 86, energizing the coil. This closes the connection between terminal 30 (battery positive) and terminal 87, sending power to the fog lights. This is a simple yet incredibly effective use of the relay's capabilities as depicted in an 87 relay wiring diagram.
For practical application and visual confirmation of these principles, refer to the detailed diagrams provided within the source material that inspired this explanation.