Understanding the 87 Relay Wiring Diagram is crucial for anyone working with automotive electrical systems or designing custom circuits. This diagram serves as a blueprint, detailing how a specific type of relay, known as a changeover or SPDT (Single Pole Double Throw) relay, is connected to control various electrical components. Whether you're troubleshooting a faulty accessory or building a new system, a clear grasp of the 87 Relay Wiring Diagram ensures correct and safe operation.
What is an 87 Relay Wiring Diagram and How is it Used?
An 87 Relay Wiring Diagram specifically illustrates the connections for a relay that has five terminals: a common terminal, a normally open (NO) terminal, a normally closed (NC) terminal, and two control terminals (usually labeled 30 and 85 or 30 and 86). The "87" in the name refers to the terminal that is energized when the relay coil is activated. This type of relay acts as an electrically operated switch. A small current applied to the coil (terminals 85 and 86) creates a magnetic field, which then moves an internal armature. This armature is responsible for connecting or disconnecting the common terminal (30) to either the normally open (87) or normally closed (86) terminal.
The primary function of an 87 Relay Wiring Diagram is to show how to leverage this switching capability to control higher-current devices with a low-current signal. This is incredibly useful because it prevents the delicate switches or control modules from being overloaded. For instance, you might use a low-current switch on your dashboard to activate the relay, which in turn powers a high-amperage device like a horn, fog lights, or an electric fuel pump. The 87 Relay Wiring Diagram guides you on which wire goes to which terminal to achieve the desired outcome. Here's a breakdown of the typical terminals and their roles:
- Terminal 30 (Common): This is the input power terminal, often connected directly to the battery or a fused power source.
- Terminal 85/86 (Coil): These terminals receive the low-current signal that energizes the relay coil. One is typically connected to ground, and the other to the control signal (e.g., from a switch or ECU).
- Terminal 87 (Normally Open): This terminal is disconnected from Terminal 30 when the relay coil is de-energized. It becomes connected when the coil is energized. This is where the power to your accessory will go when the relay is active.
- Terminal 87a (Normally Closed): This terminal is connected to Terminal 30 when the relay coil is de-energized. It becomes disconnected when the coil is energized. This terminal is less commonly used in basic accessory applications but can be useful for fail-safe circuits or switching between two devices.
The 87 Relay Wiring Diagram is essential for ensuring that the power flow is directed correctly. A common application is to power a high-draw accessory. You would connect the battery's positive terminal to terminal 30 of the relay. Then, terminal 85 would go to ground, and terminal 86 would connect to a switch. The accessory would then be connected to terminal 87. When the switch is activated, current flows through the relay coil, energizing it and causing terminal 30 to connect to terminal 87, thus powering the accessory. The importance of correctly interpreting and implementing the 87 Relay Wiring Diagram cannot be overstated, as incorrect wiring can lead to blown fuses, damaged components, or even fire hazards.
To help visualize these connections, consider this simple table outlining a typical setup for powering fog lights:
| Relay Terminal | Connection | Purpose |
|---|---|---|
| 30 | Fused Battery Positive (+) | Main power input |
| 85 | Ground (-) | Completes the coil circuit |
| 86 | Dash Switch (through fuse) | Activates the relay coil |
| 87 | Fog Lights (+) | Power output to accessory |
If you're working on a project that requires precise electrical control, understanding how to read and apply an 87 Relay Wiring Diagram is a vital skill. It provides the specific guidance needed to make reliable connections.
For a comprehensive guide and detailed illustrations of the 87 Relay Wiring Diagram, refer to the detailed schematics available in automotive repair manuals and reputable electrical component documentation.