Ignition Switch (Multi-Position) Symbol
Definition: The Ignition Switch (Multi-Position) symbol represents a key-operated rotary switch in an automotive or small-engine electrical system that sequentially connects the battery supply (BATT) to Accessory (ACC), ignition-ON (ON), and engine-START (START) circuits, shown in wiring diagrams as a four-terminal device with BATT input and ACC, ON, and START output terminals per DIN 72552 automotive wiring conventions and SAE J1858.
Also known as: key switch, key-start switch, automotive ignition switch, start switch, run/start switch, ignition lock switch.
What the Ignition Switch (Multi-Position) symbol means
The Ignition Switch (Multi-Position) symbol denotes a multi-position rotary switch actuated by an ignition key that controls which circuits receive battery power depending on the key's angular position. In a vehicle wiring diagram, the switch symbol identifies the device that sequences power delivery across four electrical states: OFF (all loads disconnected), ACC (accessories powered without engine running), ON/RUN (all ignition-dependent systems including fuel pump, ECU, gauges, and coil energised), and START (starter motor energised momentarily while all other loads remain connected).
The four-terminal representation — BATT (common battery input), ACC (accessory output), ON (run output), and START (starter solenoid output) — maps directly to the physical pin connections on the back of the ignition switch barrel. The START position is spring-loaded and momentary; it returns to ON when the key is released after the engine fires.
How to identify the Ignition Switch (Multi-Position) symbol
The ignition switch symbol is drawn as a rectangle or rotary-switch block with one input terminal on the left labelled BATT and three output terminals on the right labelled ACC (top), ON (middle), and START (bottom). Internal routing lines within the rectangle or adjacent position table show which output terminals are connected to BATT in each key position. Some schematics show the switch as a cam-operated contact matrix with rows for each key position (OFF, ACC, ON, START) and columns for each output terminal.
Function in a circuit
The ignition switch mechanically routes the battery positive supply to different output circuits depending on key position: in ACC, it connects BATT to ACC only, powering radio, power windows, and interior accessories without energising the ignition system; in ON, it connects BATT to both ACC and ON, energising the ECU, fuel pump relay, instrument cluster, and ignition coil for normal engine operation; in START, it connects BATT to ON and momentarily to START, energising the starter motor solenoid to crank the engine. A separate inhibitor or neutral safety switch in series with the START circuit prevents engine cranking in gear on automatic-transmission vehicles.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 represents multi-position rotary switches as a switch symbol with a rotating contact element indicating position-dependent connections. Automotive ignition switches follow DIN 72552 terminal numbering as the international de-facto automotive standard. IEC 60947 covers low-voltage switchgear and controlgear for the general switch functions. |
|---|---|
| ANSI/IEEE 315 | SAE J1858 (automotive wiring diagram symbols) and SAE J1292 (automobile, truck, and bus wiring) govern automotive ignition switch representation in North American drawings. ANSI/IEEE 315-1975 covers general multi-position switch symbols. The switch contact matrix convention shows which contacts close at each switch position. |
| Key difference | DIN 72552 (adopted internationally as the dominant automotive terminal standard) defines specific terminal numbers: 30 (battery), 15 (ignition ON output), 15a (ignition ON secondary), 75 (accessory), and 50 (starter). SAE/ANSI North American schematics may use descriptive labels (BATT, ACC, ON, START) rather than DIN numbers. The functional circuit is identical; only the labelling convention differs. |
Terminals / pins
| Pin | Name |
|---|---|
| batt | BATT |
| acc | ACC |
| on | ON |
| start | START |
Typical values
Battery input voltage: 12 V DC (12 V systems) or 24 V DC (heavy-duty trucks, buses). Current rating: 30 A typical (main switch contact), often with relay assistance for high-current loads. Number of positions: 4 (OFF, ACC, ON, START) standard; 3 (OFF, ON, START) on simpler vehicles. Contact resistance: <50 mΩ (new). Operating temperature: −40 °C to +85 °C.
Where the Ignition Switch (Multi-Position) symbol is used
- Passenger car ignition: key-operated four-position switch controlling accessory, run, and start circuits for the engine, ECU, and dashboard systems
- Light truck and SUV: same four-position configuration with additional outputs for glow plug preheat circuit (diesel) or 4WD transfer case control on the ON position
- Heavy-duty truck / commercial vehicle: 24 V DC ignition switch per DIN 72552, often combined with a separate master battery disconnect switch for load shedding
- Marine outboard motor: keyswitch activating kill-switch interlock, choke, and starter circuits on the engine; designed to be splash-proof for marine environments
- Generator set control panel: key-start ignition switch initiating the generator's crank/run sequence, with an engine-stop relay on the OFF position
- ATV, motorcycle, and small engine equipment: compact key switch or push-button ignition controlling magneto kill, fuel petcock, and starter circuits
Example
In a passenger car wiring diagram, the ignition switch symbol shows the BATT terminal receiving 12 V from the fusible link bus. Turning the key to ACC connects BATT to the ACC output, powering the radio and interior fan. Turning to ON connects BATT to ACC and ON, energising the fuel pump relay, ECU, and instrument cluster. Momentarily turning to START also connects BATT to START, which energises the starter motor relay. Releasing the key back to ON allows the engine to run normally.
Key facts
- The Ignition Switch (Multi-Position) symbol has four terminals: BATT (battery supply input), ACC (accessory output), ON (ignition-run output), and START (momentary starter output).
- DIN 72552 is the international automotive terminal numbering standard; it labels ignition switch connections as terminal 30 (battery), 15 (ignition ON), 75 (accessory), and 50 (starter).
- The START position is spring-loaded and momentary — it returns automatically to the ON position when the key is released after the engine starts.
- A neutral safety switch (automatic transmission) or clutch switch (manual transmission) is connected in series with the START terminal to prevent engine cranking unless the transmission is in Park/Neutral or the clutch is depressed.
- Modern vehicles replace the mechanical ignition switch with a push-button start and electronic smart key system, but the same four electrical states (OFF, ACC, ON, START) are maintained by the body control module (BCM).
- Ignition switch contacts must handle the full current draw of all energised circuits; typical ratings are 30 A continuous, though high-current loads (starter, headlights) are usually relay-switched through the ACC and ON contacts.
- Ignition switch failure is diagnosed by measuring voltage at the ACC, ON, and START terminals with a multimeter at each key position; no voltage at an expected terminal indicates a worn or open switch contact.
- In heavy-duty truck electrical systems (24 V), DIN 72552 terminal 15 (ignition ON) is used to command pre-heating of diesel engine glow plugs before the START position is engaged.
Diagrams that use this symbol
- ignition diagram
- ignition switch diagram
- ignition switch wiring diagram
- spark plug diagram
- motorcycle wiring diagram
- ignition coil wiring diagram
- 5 pole ignition switch wiring diagram
- ignition system diagram
Frequently asked questions
What does the ignition switch symbol mean in a wiring diagram?
The ignition switch symbol represents the key-operated multi-position rotary switch that controls which electrical circuits receive battery power at each key position (OFF, ACC, ON, START). In a wiring diagram it shows the BATT input and the ACC, ON, and START output terminals, indicating how the switch routes power to different vehicle systems.
What does the ignition switch symbol look like?
The ignition switch symbol is drawn as a rectangle with one terminal on the left (BATT) and three terminals on the right (ACC, ON, START). Internal routing lines or a position table shows which outputs connect to BATT at each key position. Some schematics show it as a cam-operated contact matrix with rows for each position.
What are the four positions of an ignition switch?
The four positions are: OFF (no outputs energised), ACC (BATT connected to ACC only — powers radio, interior accessories), ON (BATT connected to ACC and ON — energises ECU, fuel pump, instruments, coil), and START (BATT connected to ON and momentarily to START — cranks the starter motor). The START position is spring-loaded and returns to ON automatically.
What do DIN 72552 terminal numbers mean for an ignition switch?
DIN 72552 is the international automotive wiring terminal numbering standard. For the ignition switch: terminal 30 is the permanent battery supply (BATT); terminal 15 is the ignition-ON output (ON); terminal 75 is the accessory output (ACC); and terminal 50 is the momentary starter output (START). These terminal numbers are stamped on the switch body and used in European and international automotive wiring diagrams.
Why is there a neutral safety switch in series with the ignition switch START terminal?
A neutral safety switch (automatic transmission) or clutch switch (manual transmission) is wired in series with the START terminal to prevent the starter motor from engaging while the vehicle is in gear. This safety interlock prevents the vehicle from lurching forward or backward when the key is turned to START. Without it, engaging the starter in gear would cause dangerous unintended vehicle movement.
What standard defines the ignition switch symbol?
DIN 72552 is the dominant international standard for automotive terminal numbering, including ignition switch terminals. SAE J1858 covers automotive wiring diagram symbols for North American vehicles. ANSI/IEEE 315-1975 defines general multi-position switch symbols applicable to the ignition switch function.
How do I diagnose a faulty ignition switch?
With a multimeter set to DC volts, probe each output terminal (ACC, ON, START) while turning the key to each position and verifying that battery voltage appears at the correct terminal. No voltage at an expected output terminal while battery voltage is present at the BATT terminal indicates a worn or open internal contact. High resistance (>0.5 V drop) across the switch under load indicates worn contacts that require switch replacement.
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