Standard Automotive Relay Pin Numbers & Functions

Pin No. Function Description Typical Connection
30 Common (Power Input) The main power feed. Connected to battery +12 V (or 24 V in trucks). From battery or fuse box
87 Normally Open (NO) Output Connects to 30 when relay is energized — sends power to the load. To device/load (lamp, fan, horn, etc.)
87a (optional) Normally Closed (NC) Output Connected to 30 when relay is not energized. Opens when activated. Used when you need power off during activation
85 Coil Ground One side of the control coil. To ground (–) or ECU ground
86 Coil Positive The other side of the control coil. Receives trigger voltage (+12 V). From switch, ECU, or ignition source

🔹 Typical Relay Types

Relay Type Pins Description
SPST (Single Pole, Single Throw) 4 pins (30, 85, 86, 87) Simple on/off relay (most common).
SPDT (Single Pole, Double Throw) 5 pins (30, 85, 86, 87, 87a) Adds one normally closed (NC) output.
Dual Output Relay 5 pins (30, 85, 86, 87, 87) Has two NO outputs (both powered when activated). Often used for headlights/fans.

🔹 Typical Wiring Example

If you’re wiring a 4-pin relay for a light:

When the switch is turned on, coil (85–86) energizes → 30 connects to 87 → light turns on.

Common Flasher Unit Terminal Codes and Meanings

Terminal Full Name Function Typical Connection
B Battery / Power Input Supplies power to the flasher circuit. From ignition switch or fuse box (+12 V or +24 V).
L Load / Output Sends pulsing power to the indicator lamps (via turn signal switch). To left/right indicator switch or hazard switch.
E Earth / Ground Provides ground connection for electronic flashers. To chassis ground (–).
P Pilot / Panel Lamp Drives the dashboard indicator light (flashes in sync). To instrument cluster indicator.
C Common / Control Sometimes used as an input from the indicator switch (in 4- or 5-pin flashers). From signal or hazard switch output.
X Power Input (Alternate to B) Same as B — used mostly in European style markings. +12 V from battery/ignition.
49 Battery (German DIN code) Equivalent to B/X — power input. From fuse/ignition source.
49a Load (DIN code) Equivalent to L — flashing output. To turn signal switch or hazard relay.
31 Earth (DIN code) Equivalent to E — ground terminal. To chassis ground.
C2 Second Pilot Output For vehicles with dual dash indicators. To second indicator light.

🔹 Typical Configurations

Type Terminals Description Common Use
2-Pin Flasher B, L Simple thermal type — no ground. Older cars/motorcycles.
3-Pin Flasher B, L, E Adds ground for stable electronic control. Most modern 12 V flashers.
4-Pin Flasher B, L, E, P Adds dashboard pilot lamp output. Cars with separate indicator lamp.
5-Pin Flasher B, L, R, E, P or 49, 49a, C, C2, 31 Controls left/right indicators and dash lights independently (used in Toyota, Isuzu, heavy trucks). Trucks, buses, advanced systems.