Relay Pinout 30, 85, 86, 87, 87a — How a Car Relay Works
All CarsGeneral GuidesAll yearsPower & FusesUpdated 2026-10-10A relay is a switch worked by a small electromagnet. A small current (from a switch or computer) turns on the coil, and the coil pulls a contact that switches a big current to a fan, horn, fuel pump or lamp. Most car relays use the same pin numbers.
Pinout — pin number & wire colour
Standard automotive relay (ISO / DIN numbering)
| Pin | Name | What it does |
|---|---|---|
| 30 | COM | Main power in (from battery / fuse). |
| 85 | COIL− | Coil side — usually goes to ground (or to the ECU). |
| 86 | COIL+ | Coil side — gets +12 V from the switch. |
| 87 | NO | Output to the load when the relay is ON. |
| 87a | NC | Output when the relay is OFF (5-pin relays only). |
Relay circuit
- A switch (or the ECU) sends a small current to pin 86.
- Current flows through the coil and out of pin 85 to ground — the coil becomes a magnet.
- The magnet pulls the contact from 87a over to 87, connecting pin 30 to pin 87.
- Big current flows from the fuse, through 30 → 87, to the load (fan, horn, pump…).
🧰 Tools you need
- Digital multimeter
- OBD2 scanner (ELM327 or better)
- 12 V test light
- Back-probe pins / jumper wires
Common problems & quick checks
| Problem | Likely cause | What to check |
|---|---|---|
| Relay clicks but load doesn't work | Burnt contacts, no power on 30, or load fault | Check 12 V on pin 30. Relay ON: check 12 V on pin 87. |
| Relay doesn't click | No signal on 86, no ground on 85, or open coil | Measure coil 85–86: usually about 50–120 Ω. Check 86 gets 12 V when switched ON. |
| Quick test | — | Swap with an identical relay from another circuit (e.g. horn). If the fault moves, replace the relay. |
Related trouble codes
This is a simplified drawing for learning. Pin numbers and colours can change by model and year — check the service manual for your exact car before repairing.