Trailer Connector (4-pin Flat) Symbol
Definition: The Trailer Connector (4-pin Flat) symbol represents a standardised four-circuit electrical connector used to interface a tow vehicle's lighting system with a trailer, drawn as four parallel terminals labelled Ground (white), Tail/Running Lights (brown), Left Turn/Brake (yellow), and Right Turn/Brake (green), as specified by SAE J2863 and widely adopted in North American light-duty trailer wiring.
Also known as: 4-pin flat connector, 4-way flat connector, trailer light connector, four-pin trailer plug, flat four connector.
What the Trailer Connector (4-pin Flat) symbol means
The 4-pin flat trailer connector symbol denotes the most common light-duty trailer wiring interface in North America, providing the four circuits needed to operate basic trailer lighting: running lights, left combined turn/brake light, right combined turn/brake light, and a chassis ground return. The flat blade configuration ensures simple plug-and-play connection and is compatible with the vast majority of light utility trailers, boat trailers, and small cargo trailers.
In a wiring diagram the 4-pin flat symbol marks the electrical handoff point between the vehicle harness and the trailer harness. Each pin is colour-coded and function-labelled so that installers and inspectors can verify correct wiring without a meter. The connector does not provide a dedicated circuit for electric trailer brakes, reverse lights, or auxiliary 12 V power — loads that require a 5-, 6-, or 7-pin connector.
How to identify the Trailer Connector (4-pin Flat) symbol
The 4-pin flat connector symbol is drawn as a rectangular housing containing four evenly-spaced rectangular or circular blade contacts arranged in a single horizontal row. Pin labels are placed above or below each contact: from left to right the standard order is Ground (white wire), Tail/Running Lights (brown wire), Left Turn/Brake (yellow wire), Right Turn/Brake (green wire). The housing outline may include a locking tab or a flat moulded body profile to distinguish it from round multi-pin connectors.
Function in a circuit
The 4-pin flat connector transfers four electrical circuits from the tow vehicle to the trailer: the Ground pin (white) provides a common chassis return for all trailer circuits; the Tail pin (brown) carries the running-light and side-marker signal; the Left Turn pin (yellow) carries the combined left turn signal and left brake light signal; and the Right Turn pin (green) carries the combined right turn signal and right brake light signal. The connector is rated for low-current lighting loads (typically < 10 A per pin) and is not suitable for electric brake controllers or high-current auxiliary loads.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60309 defines industrial and commercial multipole connectors but does not specify the 4-pin flat trailer format. Trailer connector types used in Europe are governed by ISO 1724 (7-pin round) or ISO 11446 (13-pin), not the flat 4-pin format. |
|---|---|
| ANSI/IEEE 315 | SAE J2863 (United States) defines trailer towing electrical connectors including the 4-pin flat configuration. ASABE S390 covers additional North American trailer wiring standards. The colour codes match FMVSS 108 signal functions. |
| Key difference | The 4-pin flat connector is a North American standard (SAE J2863) and has no direct IEC equivalent; European trailers use the ISO 1724 7-pin round connector. The flat body and blade contacts are mechanically incompatible with European round-pin connectors. |
Terminals / pins
| Pin | Name |
|---|---|
| gnd | Ground (white) |
| tail | Tail (brown) |
| lt | Left Turn (yellow) |
| rt | Right Turn (green) |
Typical values
Maximum current per pin: 10 A (SAE J2863 for lighting circuits). Operating voltage: 12 V DC. Temperature range: typically −40 °C to +85 °C. Wire gauge: typically 18–14 AWG. Connector housing material: nylon or polypropylene, UV-stabilised. IP rating: IP54 (splash-resistant when mated).
Where the Trailer Connector (4-pin Flat) symbol is used
- Light utility trailer wiring — open-deck and box trailers up to 3,500 lb GVWR use the 4-pin flat connector for running lights, brake lights, and turn signals.
- Boat trailer lighting — single-axle boat trailers use the 4-pin flat to connect trailer lighting to the tow vehicle without the complexity or cost of a larger connector.
- Landscape and garden trailer — small dump trailers and equipment trailers with only lighting requirements (no electric brakes) use the 4-pin flat as the simplest and lowest-cost option.
- Motorcycle and ATV trailers — small tow-behind trailers for recreational vehicles use the 4-pin flat because the towing motorcycles and ATVs use the same colour-coded four-circuit wiring harness.
- OEM vehicle trailer prep packages — many pickup trucks and SUVs include a factory-installed 4-pin flat pigtail on the tow hitch harness, making the connector the default interface for light-duty towing.
- Rental and hire trailers — standardised 4-pin flat connectors on hire trailers ensure compatibility with any vehicle that has a basic 4-pin tow hitch wiring harness, without the need for adapters.
Example
In a wiring diagram for a single-axle utility trailer, the 4-pin flat connector symbol is placed at the hitch end of the trailer harness. From the Ground (white) pin, a white wire runs to the trailer frame. The Tail (brown) pin feeds both the licence plate lamp and the running-light filaments on each tail lamp. The Left (yellow) and Right (green) pins each feed the appropriate combined turn/brake lamp filament. The vehicle side shows the mating socket symbol connected to the factory tail-light harness via a T-connector tap.
Key facts
- The 4-pin flat trailer connector provides four circuits: Ground (white), Tail/Running Lights (brown), Left Turn/Brake (yellow), and Right Turn/Brake (green) — the minimum circuits required for legal trailer lighting in North America.
- The connector follows the colour-code scheme of SAE J2863 and FMVSS 108: white = ground, brown = running/tail, yellow = left turn/brake, green = right turn/brake.
- The flat blade body design ensures a single correct mating orientation, preventing reverse insertion and incorrect circuit connections.
- The 4-pin flat connector does NOT support electric trailer brakes, reverse lights, or 12 V auxiliary power — applications requiring those circuits need a 5-pin, 6-pin, or 7-pin connector.
- Maximum rated current is 10 A per pin under SAE J2863, sufficient for incandescent or LED trailer lighting but not for brake controllers (which require a dedicated brake-output pin on a larger connector).
- Pins on this symbol: Ground (white, x=14 y=25), Tail (brown, x=24 y=25), Left Turn (yellow, x=34 y=25), Right Turn (green, x=44 y=25).
- The European equivalent for trailer electrical connection is the ISO 1724 7-pin round connector; the North American 4-pin flat is mechanically incompatible with European standards.
- A T-one connector (or T-harness) is the most common vehicle-side installation method: it plugs in-line with the tail-lamp socket on the tow vehicle, extracting the four lighting signals without cutting factory wires.
Frequently asked questions
What does the 4-pin flat trailer connector symbol look like?
The 4-pin flat connector symbol shows a rectangular housing with four evenly-spaced blade contacts in a single row, labelled left to right as Ground (white), Tail (brown), Left Turn (yellow), and Right Turn (green). The flat body shape distinguishes it from round multi-pin trailer connectors.
What does each pin on a 4-pin flat trailer connector do?
Ground (white) is the chassis return for all circuits. Tail (brown) carries the running lights and licence plate lamp signal. Left Turn/Brake (yellow) carries the combined left indicator and brake signal. Right Turn/Brake (green) carries the combined right indicator and brake signal. The turn and brake functions are combined on yellow and green because the tow vehicle's tail-light circuit combines them.
What is the colour code for a 4-pin flat trailer connector?
The standard colour code per SAE J2863 is: white = ground, brown = running/tail lights, yellow = left turn and brake, green = right turn and brake. This colour scheme is consistent across virtually all North American light-duty trailer connectors and matches the FMVSS 108 signalling requirements.
What standard governs the 4-pin flat trailer connector?
The 4-pin flat trailer connector is specified in SAE J2863 (Trailer Towing Electrical Connectors) for North American use. ASABE S390 covers additional agricultural trailer wiring. European trailer connectors are governed by ISO 1724 (7-pin) and are not interchangeable with the flat 4-pin format.
Can I use a 4-pin flat connector for electric trailer brakes?
No. The 4-pin flat connector does not include a dedicated brake-controller output pin. Electric trailer brakes require at least a 5-pin flat or 7-pin round connector that includes a separate brake-control wire (typically blue). Using a 4-pin connector with electric brakes is not wired correctly and the brakes will not function.
What is the difference between a 4-pin flat and a 7-pin round trailer connector?
The 4-pin flat connector provides only the four basic lighting circuits (ground, tail, left, right) and is used for light trailers without brakes or auxiliary power. The 7-pin round connector (SAE J560 / RV-style) adds circuits for electric brakes, reverse lights, and a 12 V auxiliary supply, making it suitable for heavy trailers, RVs, and horse trailers. The two connector types are mechanically incompatible but adapters are available.
How do I wire a 4-pin flat trailer connector to my tow vehicle?
The easiest method is a T-one (T-harness) connector that plugs into the existing tail-light socket on the vehicle without cutting wires. The T-harness extracts the four signals and provides a 4-pin flat socket at the hitch. Alternatively, a direct-wire kit connects to the vehicle's existing tail-light wires using the SAE J2863 colour code: white to ground/chassis, brown to running lights, yellow to left turn/brake, green to right turn/brake.
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