Relay Pinout Diagrams Explained

A relay pinout diagram shows the function of each terminal (pin) on a relay and how the internal connections work. It helps you wire the relay correctly for your project.

1. Basic Relay Anatomy

Most automotive relays have two main parts:

• Coil – An electromagnet that switches the relay on/off (low current side)
• Switch Contacts – The high-current switch that turns your accessory on/off

2. Most Common Automotive Relay: 5-Pin SPDT

This is the standard relay type used with sockets like BRSCN, BRSPC, BRSS, etc.

Visual Pinout Diagram

          87
          │
   87a ───┼─── 30
          │
         [Relay]

   85 ───────── 86
    

How It Works:

• No power to 85/86 → Current flows between 30 and 87a
• +12V applied to 85/86 → Coil energizes → Current flows between 30 and 87

4. How to Read a Relay Pinout Diagram

Most relay pinout diagrams include the following elements:

• A box or outline representing the relay body
• Pin numbers clearly labeled next to each terminal
• Internal connections shown with lines or dotted lines
• Coil symbol (usually a rectangle or spring-like coil)
• Switch contacts shown with an arrow indicating movement when the relay is energized

Example Relay Pinout Diagram:

       87          30
        │           │
        └──────┬────┘
               │
             ┌──┐     ← Moving Contact
             └──┘
            /     \
          87a      (Switches when coil is energized)

    85 ───────────── 86
          Coil
    

Understanding the Symbols:

• 30 — Common terminal (input power)
• 87 — Normally Open (NO) contact
• 87a — Normally Closed (NC) contact
• 85 & 86 — Coil terminals (control side)

When the relay coil is energized (pins 85/86 powered), the internal switch moves from 87a to 87.

Quick Wiring Examples (5-Pin Relay)

1. Basic On/Off Circuit (Most Common)

Used for lights, fans, fuel pumps, horns, etc.

• 86 → Switched +12V (from switch, toggle, or ECU output)
• 85 → Ground (or switched ground)
• 30 → Constant +12V Power (from battery or fuse box)
• 87 → Output to Accessory (lights, fan, etc.)
• 87a → Not used (leave disconnected)

2. Changeover / Dual Circuit Setup

Use both 87 and 87a when you need to switch between two different circuits.

• 30 → Input Power
• 87 → Circuit A (ON when relay is energized)
• 87a → Circuit B (ON when relay is OFF)
• 85 & 86 → Coil control

3. Typical Pin Connections Summary

Tip: Always use a fused power source on pin 30 for safety.

Basic 5-Pin Relay Wiring Harness

Battery +12V ──► [Fuse] ──► Pin 30 (Common)

Pin 87 ──► Accessory (Lights / Fan / Pump / Amp etc.)

Pin 86 ──► Switched +12V Trigger
               (from switch, headlight wire, remote turn-on, etc.)

Pin 85 ──► Ground

Pin 87a ──► (Optional - Not used in basic setup)
    

Recommended Wiring (Empty relay socket or spade connectors (Not BRS14E & BRS12E):

• Pin 30 — Red wire with inline fuse (closest to battery)
• Pin 87 — Red or Blue wire to device
• Pin 86 — White or Pink trigger wire
• Pin 85 — Black ground wire

Dual Output (Changeover) Relay Harness

Pin 30   → Constant +12V (Fused)

Pin 87   → Circuit A (ON when relay activated)
Pin 87a  → Circuit B (ON when relay is off)

Pin 86   → Trigger +12V
Pin 85   → Ground