Trailer Connector (7-pin) Symbol
Definition: The Trailer Connector (7-pin) symbol represents a seven-circuit round electrical connector used to interface a tow vehicle with a heavy-duty trailer, drawn as a circular housing with seven terminals labelled 12V+/Aux, Brake, Right Turn, Ground, Tail, Left Turn, and Reverse, as specified by SAE J560 (commercial) or the RV-industry standard widely used for caravans, horse trailers, and fifth-wheel applications.
Also known as: 7-pin round connector, 7-way trailer connector, RV trailer connector, 7-pin trailer plug, SAE J560 connector, caravan connector.
What the Trailer Connector (7-pin) symbol means
The 7-pin trailer connector symbol denotes the full-function electrical interface between a tow vehicle and a trailer that requires electric brakes, reverse lights, and a 12 V auxiliary power supply in addition to the four basic lighting circuits. The seven pins correspond to all circuits needed for a fully independent trailer electrical system, including brake-controller output, reverse lamps, and battery charging or refrigerator power for caravans and RVs.
In a wiring diagram the 7-pin connector symbol marks the boundary between the vehicle harness and the trailer harness. Each pin is identified by colour code and function, allowing installers to connect circuits correctly. The circular housing with a keyway ensures the plug can only be inserted in one orientation, preventing misconnection of the brake or auxiliary power circuits.
How to identify the Trailer Connector (7-pin) symbol
The 7-pin round connector symbol is drawn as a circle representing the round housing, with seven contacts arranged in a specific pattern around the interior. Pin positions follow the SAE J560 or RV-industry keying: the 12V+/Aux pin is at the top (12 o'clock), with Brake and Right Turn at the upper right, Ground at the centre or specific position, Tail at the bottom, Left Turn at the left, and Reverse at the upper left. A flat side or keyway on the housing outline indicates the connector orientation. Labels or colour annotations identify each pin function.
Function in a circuit
The 7-pin connector distributes seven independent circuits: 12V+/Aux (pin 1, typically black or red wire) provides 12 V battery charging or auxiliary power to the trailer; Brake (pin 2, blue wire) carries the electric brake controller output signal to the trailer's electric brake assemblies; Right Turn/Brake (pin 3, green wire) carries the right indicator and right stop-light signal; Ground (pin 4, white wire) provides the chassis return for all circuits; Tail/Running Lights (pin 5, brown wire) carries running lights and licence plate lamp power; Left Turn/Brake (pin 6, yellow wire) carries the left indicator and stop-light signal; Reverse (pin 7, purple wire) carries the reverse-lamp signal to illuminate the trailer's reversing lights.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60309 defines industrial multipole connectors but does not specify the 7-pin round trailer format. European caravan connectors are governed by ISO 1724 (7-pin round, different keyway and pin assignment from SAE J560) and ISO 11446 (13-pin). |
|---|---|
| ANSI/IEEE 315 | SAE J560 defines the 7-pin round connector for commercial truck and trailer use in North America. The RV-industry '7-way' connector shares the circular form factor and most pin assignments with J560 but with minor variations. ASABE S390 covers agricultural trailer wiring using this connector format. |
| Key difference | The North American SAE J560 7-pin round and the European ISO 1724 7-pin round connectors are physically similar (both round, 7-pin) but have different keyways and different pin assignments, making them mechanically and electrically incompatible without an adapter. The North American connector uses a flat keying tab while the European version uses a different offset position. |
Terminals / pins
| Pin | Name |
|---|---|
| aux | 12V+/Aux |
| brake | Brake |
| rt | Right Turn |
| gnd | Ground |
| tail | Tail |
| lt | Left Turn |
| reverse | Reverse |
Typical values
Maximum current: 20–30 A on the 12V+/Aux circuit; 7–20 A on brake and lighting circuits (SAE J560). Operating voltage: 12 V DC. Temperature range: −40 °C to +85 °C. Wire gauge: 12–14 AWG for brake and auxiliary power; 16–18 AWG for lighting signals. Connector body: glass-filled nylon, UV-stabilised. IP rating: IP54 when mated.
Where the Trailer Connector (7-pin) symbol is used
- Fifth-wheel and gooseneck trailers — heavy tow configurations require all 7 circuits including electric brakes, reverse lamps, and battery charging via the aux pin for the trailer's internal electrical loads.
- Horse trailers and livestock trailers — electric brakes on multiple axles, interior lighting, and water pump power require the 12V+/Aux and brake circuits provided by the 7-pin connector.
- Caravan and RV towable units — the 12V+/Aux circuit powers the caravan's battery charger, refrigerator, and interior lighting while driving; the brake circuit operates the caravan's electric brakes on steep descents.
- Boat trailers with electric brakes — larger boat trailers over 3,500 lb often use surge brakes or electric brakes requiring the dedicated brake-controller circuit on pin 2 (blue) of the 7-pin connector.
- Commercial flatbed and semi-trailer connections — commercial vehicles use the SAE J560 7-pin connector to interface tractor lighting harnesses with trailer lighting, ABS modulator connectors, and refrigeration unit power.
- Vehicle-mounted equipment trailers — military, utility, and emergency-service tow vehicles use the 7-pin connector to power lighting and electric brakes on equipment trailers and generator trailers.
Example
In a wiring diagram for a horse trailer, the 7-pin round connector symbol sits at the front of the trailer tongue. The 12V+/Aux (black) pin feeds a 15 A automotive fuse then connects to the trailer's 12 V distribution bus, powering interior lights and a water pump. The Brake (blue) pin feeds the two electric brake assemblies via the brake-controller output on the tow vehicle. The Tail (brown) and Left/Right Turn pins (yellow/green) feed the four combination tail-lamp assemblies. The Reverse (purple) pin illuminates two rear-facing white lamps when the transmission is in reverse.
Key facts
- The 7-pin round trailer connector provides seven circuits: 12V+/Aux (black), Brake controller (blue), Right Turn/Brake (green), Ground (white), Tail/Running Lights (brown), Left Turn/Brake (yellow), and Reverse lights (purple).
- The blue Brake wire carries the electric brake controller output — a proportional voltage (0–12 V) that applies the trailer's electric brakes in proportion to the tow vehicle's deceleration, as required by law for trailers above a defined weight.
- SAE J560 governs the North American commercial 7-pin round connector; the European equivalent is ISO 1724, which uses the same round form factor but a different pin assignment and keyway — the two standards are incompatible.
- The 12V+/Aux (typically black or red) circuit is fused at the vehicle side (usually 20–30 A) and charges the trailer's onboard battery while driving, or powers refrigerators and interior loads in caravan applications.
- The connector housing has a keyway that allows insertion in only one orientation, preventing the brake or aux power pins from being connected to the wrong vehicle circuits.
- Pins on this symbol: 12V+/Aux (x=30 y=15), Brake (x=48 y=22), Right Turn (x=48 y=48), Ground (x=30 y=35), Tail (x=30 y=55), Left Turn (x=12 y=48), Reverse (x=12 y=22).
- A 7-pin to 4-pin adapter is widely available for towing light trailers from a vehicle equipped with a 7-pin socket, but such an adapter does NOT add brake or auxiliary circuits to a 4-pin trailer harness.
- Electric brakes on a trailer legally require a brake controller in the tow vehicle (required for trailers over 1,500 kg in many jurisdictions); the blue wire on the 7-pin connector carries the brake-controller output signal to each brake assembly.
Diagrams that use this symbol
- trailer wiring diagram
- 7 pin trailer wire
- seven pin trailer wiring
- seven pin trailer plug
- trailer plug 7 pin
- trailer connector wiring
- wiring a trailer plug
- trailer light wiring diagram
Frequently asked questions
What does the 7-pin trailer connector symbol look like?
The 7-pin connector symbol is a circle representing the round housing, with seven contacts arranged at specific clock positions inside. A keyway notch on one side indicates orientation. Each pin is labelled with its function: 12V+/Aux at top, Brake at upper right, Right Turn at right, Ground at centre-right, Tail at bottom, Left Turn at left, Reverse at upper left.
What is each pin on a 7-pin trailer connector used for?
Pin 1 (black or red, 12V+/Aux): 12 V power for battery charging and auxiliary loads. Pin 2 (blue, Brake): electric brake controller output. Pin 3 (green, Right Turn/Brake): right indicator and stop light. Pin 4 (white, Ground): chassis return. Pin 5 (brown, Tail): running and tail lights. Pin 6 (yellow, Left Turn/Brake): left indicator and stop light. Pin 7 (purple, Reverse): reverse lamps.
What is the colour code for a 7-pin round trailer connector?
The North American SAE J560 colour code is: black = 12V+/Aux, blue = brake controller, green = right turn/brake, white = ground, brown = tail/running, yellow = left turn/brake, purple = reverse. This colour scheme is consistent across RV-style 7-pin connectors and matches FMVSS 108 signalling requirements.
What is the difference between a 7-pin and 4-pin trailer connector?
The 4-pin flat connector provides only the four basic lighting circuits (ground, tail, left, right) and cannot support electric brakes, reverse lights, or auxiliary 12 V power. The 7-pin round connector adds three more circuits: a brake-controller output (blue), reverse lights (purple), and 12 V auxiliary power (black), making it necessary for any trailer with electric brakes or internal electrical loads.
Are North American and European 7-pin trailer connectors interchangeable?
No. The North American SAE J560 7-pin round connector and the European ISO 1724 7-pin round connector look similar but have different pin assignments and different keyways, making them mechanically and electrically incompatible. An adapter is required to tow a European-wired trailer with a North American-wired vehicle, and the brake circuits must be re-mapped carefully.
Does the 7-pin connector charge the trailer battery?
Yes — the 12V+/Aux pin (black wire, pin 1) supplies 12 V from the vehicle's charging system to the trailer when the vehicle is running. This charges the trailer's onboard battery and can power refrigerators, interior lights, and ventilation fans in caravans and RVs. The circuit is typically fused at 20–30 A on the vehicle side.
What standard governs the 7-pin trailer connector?
SAE J560 governs the 7-pin round connector for commercial trucks and trailers in North America. The RV industry uses a similar but slightly variant 7-way connector often called the 'RV blade' type. In Europe, ISO 1724 defines the 7-pin round connector for caravans and light trailers, while ISO 11446 covers the 13-pin connector for more modern European caravans.
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