Automotive Relay (5-pin) Symbol
Definition: The Automotive Relay symbol represents the standard 12 V SPDT 'mini' (Bosch-style) relay used throughout vehicle wiring, drawn as a box containing a coil and a changeover contact with terminals numbered to DIN 72552 — 85 and 86 for the coil, 30 for the common contact feed, 87 for the normally-open output, and 87a for the normally-closed output.
Also known as: Bosch relay, ISO mini relay, 5-pin relay, 12V automotive relay, SPDT automotive relay, changeover relay, cube relay, 30/40A relay.
What the Automotive Relay (5-pin) symbol means
The Automotive Relay symbol denotes an electromagnetic switch that lets a small control current — from an ignition switch, dash button, or ECU output rated for a fraction of an amp — command a heavy load current of 20–40 A or more to headlights, horns, fuel pumps, or fans. Energizing the coil between terminals 86 (Coil+) and 85 (Coil−) magnetizes an armature that pulls the movable contact from its rest position on 87a (normally closed) over to 87 (normally open), connecting the battery feed on 30 (Common) to the load. De-energize the coil and a spring returns the contact to 87a.
The DIN 72552 numbering is the whole point of the symbol's labeling: those five numbers are stamped into virtually every relay base, socket, and wiring diagram in the automotive world, making circuits readable across manufacturers. 30 is always the common/battery feed (the DIN code for battery positive), 85/86 are always the coil, 87 the NO output, 87a the NC output. A 4-pin variant omits 87a (SPST, NO only), and a common 5-pin 'dual 87' variant replaces 87a with a second 87 terminal paralleled to the first — a trap for anyone assuming every fifth pin is a normally-closed contact.
How to identify the Automotive Relay (5-pin) symbol
The symbol is a rectangle containing two distinct parts: the coil (drawn as a box, sawtooth, or coil winding between terminals 85 and 86) and the changeover contact (a pivoting contact arm on terminal 30 resting against 87a and swinging to 87). The DIN numbers beside each terminal identify everything — no other component uses the 30/85/86/87/87a set. On the physical relay the numbers are molded next to the blades, whose ISO 'mini' footprint places 30, 85, 86, 87 in a cross pattern with 87a (when present) in the center; 30 and 87 usually use wider 9.5 mm blades for the high-current path.
European (DIN/IEC-style) vehicle diagrams draw the coil as a rectangle and the contact per IEC 60617 contact symbols, while American service literature may use the circle-coil or sawtooth plus a switch arm — but both retain the DIN numbers, which are the reliable identifier. Relays with a suppression diode or resistor across the coil show it inside the box; diode-suppressed relays make coil polarity mandatory (86 must be positive).
Function in a circuit
Applying 12 V across 86 and 85 drives roughly 130–170 mA through the ~70–90 Ω coil, magnetizing the core and snapping the armature over in a few milliseconds; contact 30 leaves 87a and lands on 87, powering the load with battery current that never has to pass through the dash switch or thin control wiring. Removing coil power collapses the field and the return spring restores 30-to-87a. The coil's collapsing field generates a voltage spike of a hundred volts or more, so ECU-driven relays are suppressed with a resistor or diode across the coil (with a diode, terminal 86 must be the positive side or the diode conducts and blows the fuse).
Either coil terminal may be switched: high-side control switches +12 V to 86 with 85 grounded (the common arrangement), while ECU low-side control feeds 86 constant ignition power and grounds 85 through the module. The NC contact 87a serves loads that must run until commanded off, changeover interlocks, and flip-flop circuits such as fuel-pump priming or headlight changeover.
Standards: IEC vs ANSI
| IEC 60617 | Terminal designations follow DIN 72552 (the German automotive terminal-numbering standard adopted industry-wide): 30 battery positive/common, 85 coil end (conventionally the switched-to-ground side), 86 coil supply, 87 NO output, 87a NC output. The coil and changeover-contact graphics follow IEC 60617 relay and contact symbols; ISO 7588 defines the plug-in relay footprints. |
|---|---|
| ANSI/IEEE 315 | North American service diagrams draw the same device with ANSI Y32.2 / IEEE 315 relay symbols (coil plus SPDT contact) but retain the DIN 72552 numbers because the hardware itself is standardized around them; SAE-style diagrams may additionally name circuits (BATT, IGN) alongside the numbers. Micro (ISO 280) and mini relay footprints are shared internationally. |
| Key difference | Graphically, European diagrams use IEC-style box coils and contact bars where American ones may use coil circles and switch arms — but the DIN 72552 terminal numbers appear in both and are the universal decoder. The practical caveat is variant confusion, not symbology: a 5-pin changeover relay (87 + 87a) and a 5-pin dual-output relay (two paralleled 87s) look identical at a glance and differ only in the terminal legend. |
Terminals / pins
| Pin | Name |
|---|---|
| 85 | 85 (Coil-) |
| 86 | 86 (Coil+) |
| 30 | 30 (Common) |
| 87 | 87 (NO) |
| 87a | 87a (NC) |
Typical values
Standard 12 V mini relays: coil resistance 70–90 Ω, pulling about 130–170 mA (≈1.8 W) with pull-in around 7–8 V and drop-out around 2–4 V; contact ratings 30 A (NO)/20 A (NC) or 40/30 A at 12 V DC resistive, with micro (ISO 280) relays at 20–25 A. 24 V truck versions use ~320 Ω coils. Mechanical life exceeds 10 million operations, electrical life around 100,000 at rated load. Suppression options: ~680 Ω resistor or a diode across the coil (diode versions are polarity-sensitive: 86 positive). Blade sizes: 6.3 mm for coil terminals, often 9.5 mm for 30 and 87.
Where the Automotive Relay (5-pin) symbol is used
- Headlight, spotlight, and driving-light circuits, keeping high beam current out of the column switch
- Horn circuits, where the horn button grounds terminal 85 and the relay passes the heavy horn current
- Fuel-pump supply commanded by the ECU, often with the ECU switching the coil's ground side
- Radiator and intercooler fan control, including two-speed schemes using the 87/87a changeover
- Starter-circuit interposing relays and accessory isolation on ignition-switched feeds
- Aftermarket additions — winches, air compressors, amplifiers, light bars — wired with a relay, an inline fuse on terminal 30, and a thin switched wire to 86
Example
Wiring driving lights: a fused 12 AWG feed from the battery goes to pin 30 (Common), the lights connect to pin 87 (NO), the coil's 86 (Coil+) pin takes a thin switched wire from the dash toggle, and 85 (Coil−) goes to chassis ground — flipping the toggle drives ~150 mA through the coil, the contact snaps 30 across to 87, and the lights draw their full 15 A directly from the battery through the relay while pin 87a sits unused (or feeds a 'lights off' indicator, being closed only at rest).
Key facts
- DIN 72552 terminal decoding: 30 = common/battery feed, 85 = coil (−), 86 = coil (+), 87 = normally open output, 87a = normally closed output.
- The relay lets milliamps switch tens of amps: a ~150 mA coil current controls 30–40 A contacts, protecting switches, ECU outputs, and thin control wiring.
- 87a is connected to 30 when the relay is AT REST; energizing the coil breaks 30–87a and makes 30–87 — a true SPDT changeover.
- Beware the two 5-pin variants: changeover (87 + 87a) versus dual-output (two paralleled 87s). They look identical; only the terminal legend distinguishes them.
- Coil specs for 12 V mini relays: 70–90 Ω, ≈1.8 W, pull-in ~7–8 V, drop-out ~2–4 V; 24 V versions use ~320 Ω coils.
- The coil's inductive kick exceeds 100 V at switch-off; diode- or resistor-suppressed relays protect ECU drivers, and diode versions make polarity mandatory (86 positive).
- Terminal 30 should carry an inline fuse close to the battery — the relay switches current but provides no overcurrent protection.
- Standard footprints are the ISO mini (30/40 A, 6.3/9.5 mm blades) and ISO micro/280 (20–25 A); numbering and pinout are consistent enough that relays interchange across brands.
Frequently asked questions
What do the numbers 30, 85, 86, 87, and 87a mean on a relay?
They are DIN 72552 terminal codes, standard across the automotive industry: 30 is the common contact feed (traditionally battery positive), 85 and 86 are the two ends of the coil (conventionally 86 to switched +12 V and 85 to ground), 87 is the normally-open output that connects to 30 when the coil is energized, and 87a is the normally-closed output connected to 30 at rest. The same numbers appear on the relay body, its socket, and every wiring diagram.
How do I wire a 5-pin automotive relay for accessory lights?
Battery positive through an appropriately-rated inline fuse to 30; the lights from 87 to ground; a thin wire from a switched +12 V source (via your dash switch) to 86; and 85 to chassis ground. Leave 87a unconnected unless you need something powered only when the lights are OFF. When the switch closes, the coil energizes and 30–87 passes the full load current — the dash switch only ever carries the ~150 mA coil current.
What is the difference between a 4-pin and a 5-pin automotive relay?
A 4-pin relay is SPST: coil (85/86) plus a normally-open contact (30/87) — fine for simply switching a load on. A 5-pin relay adds a fifth terminal, but in TWO flavors: a changeover (SPDT) relay adds 87a, a normally-closed contact, enabling either/or switching; a dual-output relay instead adds a second 87 paralleled internally for feeding two loads. Check the legend printed on the relay — the two 5-pin types are physically identical otherwise.
Does coil polarity matter on terminals 85 and 86?
For a plain relay, no — the coil is just a winding and works either way, though convention puts +12 V on 86 and ground on 85. It matters absolutely for diode-suppressed relays: the internal flyback diode across the coil is oriented for 86 positive, and reversing polarity forward-biases the diode, effectively short-circuiting the coil supply and blowing the fuse or the diode. Resistor-suppressed relays remain polarity-insensitive, which is why many manufacturers prefer them.
Why use a relay at all instead of switching the load directly?
Current and voltage-drop management. A 30 A headlight or winch feed run through the dash means long, heavy cable, hot switches, and burned contacts — dash switches and ECU outputs are typically rated for a few amps at most. A relay lets the heavy current take the shortest path from battery to load through 30–87, while the human interface carries only ~150 mA of coil current on thin wire. It also isolates delicate electronics from the load circuit's noise and inductive kick.
How do I test an automotive relay?
Three steps. (1) Coil: measure resistance across 85–86 — expect roughly 70–90 Ω for a 12 V mini relay; open or near-zero means a bad coil. (2) Operation: apply 12 V across 85/86 and listen/feel for the click; verify continuity appears across 30–87 and disappears across 30–87a. (3) Under load: a relay can click yet have burned contacts, so check for voltage drop across 30–87 while the real load runs — more than a couple of tenths of a volt at rated current means worn contacts. Substituting a known-good identical relay is the fastest field test.
Related symbols
- Changeover Contact (SPDT) symbol
- Horn / Siren symbol
- Ignition Switch (Multi-Position) symbol
- Fuse symbol
- Relay Coil symbol
- Relay SPDT symbol
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