Automotive Relays & ISO Pinouts
Electrical & Ignition Standards · 9 specs
Direct Answer
Automotive electromechanical relays switch high-current vehicle loads (cooling fans, fuel pumps, headlights, starter solenoids) using low-current control signals, standardized under ISO 7588 into Mini (1-inch cube) and Micro form factors with standard DIN 72552 terminal numbering (30, 85, 86, 87, 87a).
Source: ISO 7588-1 (Mini Relays) / ISO 7588-2 (Micro Relays) / DIN 72552 · Last reviewed Aug 28, 2026
Specs
| Governing Standards | ISO 7588 / DIN 72552 / SAE J2544 |
| Form Factor Tiers | ISO Mini Relay (~28×28×25 mm) / ISO Micro Relay (~22×15×25 mm) / Maxi Relay |
| Contact Switching Ratings | Mini: 30A to 50A at 14V DC | Micro: 20A to 35A at 14V DC |
| Nominal Coil Voltages | 12V DC (automotive passenger cars) / 24V DC (heavy commercial trucks) |
| Terminal 30 (DIN 72552) | Common High-Current Power Input (Fused Battery B+ feed) |
| Terminal 85 (DIN 72552) | Relay Coil Ground / Trigger Return (connected to ECU or ground switch) |
| Terminal 86 (DIN 72552) | Relay Coil Power (+12V ignition switch or control trigger) |
| Terminal 87 (DIN 72552) | Normally Open (NO) Output — Energized when coil is activated |
| Terminal 87a (DIN 72552) | Normally Closed (NC) Output — Energized when coil is unpowered (5-pin SPDT only) |
Standard DIN 72552 Automotive Relay Terminal Schematic
| Terminal Number | Circuit Function | Wiring Connection | Standard Terminal Blade Width |
|---|---|---|---|
| Pin 30 | High-Current Power Input | Direct fused feed from Battery (+12V / +24V) | 6.3 mm (1/4") Quick-Connect Blade |
| Pin 85 | Coil Ground / Control | Ground switch or Engine Control Unit (ECU) low-side driver | 6.3 mm (or 4.8 mm on Micro relays) |
| Pin 86 | Coil Trigger Power | +12V switched ignition source or switch feed | 6.3 mm (or 4.8 mm on Micro relays) |
| Pin 87 | Normally Open (NO) Output | Connected to High-Draw Accessory (Fuel Pump, Headlight, Fan) | 6.3 mm (or 9.5 mm on high-amp Maxi relays) |
| Pin 87a | Normally Closed (NC) Output | Connected to alternate circuit (5-pin Changeover / SPDT only) | 6.3 mm Blade (Center pin on ISO Mini) |
4-Pin SPST vs 5-Pin SPDT & Flyback Diode Protection
- 4-Pin (SPST - Single Pole Single Throw): Pins 30, 85, 86, 87. Standard on/off switch for single accessories.
- 5-Pin (SPDT - Single Pole Double Throw): Adds Pin 87a in the center. Toggles power between two circuits (e.g. daytime running lights switching to low beams).
- Flyback Suppression Diode / Resistor: When an energized relay coil is suddenly disconnected, the collapsing magnetic field creates a reverse voltage spike that, left unsuppressed, can reach into the hundreds of volts (the exact peak depends on coil inductance and switching speed). Automotive relays used with delicate vehicle ECUs feature an internal parallel suppression diode or resistor across Pins 85 and 86 to dissipate inductive energy safely.