Brake and Turn Signal Wire Colors: What They Are and How to Verify

For most North American light-duty trailers, yellow is the left turn and brake light wire, and green is the right turn and brake light wire. In European/ISO trailer wiring, red is used for the brake/stop lamp, with yellow for the left indicator and green for the right indicator. Inside passenger vehicles, however, wire colors are not universal and vary by make, model, and year—always confirm with a wiring diagram or by testing.

North American Trailer Wiring (Light-Duty)

The color coding below reflects the most common standards used in the U.S. and Canada for flat, round, and RV-blade connectors. These standards combine brake and turn functions on the left and right circuits for 4- and 5-way systems, while 7-way adds more features such as electric brakes and reverse lights.

• 4-pin flat (typical small trailers)
  

  • White: Ground
  • Brown: Tail/marker/running lights
  • Yellow: Left turn & brake
  • Green: Right turn & brake

• 5-pin flat (often marine)
  

  • White: Ground
  • Brown: Tail/marker/running lights
  • Yellow: Left turn & brake
  • Green: Right turn & brake
  • Blue: Reverse/backup or surge-brake lockout (note: not the electric brake controller output)

• 6-way round (older/towing setups)
  

  • White: Ground
  • Brown: Tail/marker/running lights
  • Yellow: Left turn & brake
  • Green: Right turn & brake
  • Blue: Electric trailer brakes (controller output)
  • Black: 12V auxiliary power/charge

• 7-way RV blade (SAE J2863, common on pickups/SUVs)
  

  • White: Ground
  • Brown: Tail/marker/running lights
  • Yellow: Left turn & brake
  • Green: Right turn & brake
  • Blue: Electric trailer brakes (controller output)
  • Black: 12V battery/charge
  • Purple: Reverse/backup (center pin)

These color conventions are widely used by OEMs and aftermarket harnesses, but always verify functionally—older trailers or previous repairs may not follow the standard.

European/International Trailer Wiring (ISO Standards)

In Europe, brake and turn signals are typically separate circuits. The ISO 1724 7-pin (“12N”) and ISO 11446 13-pin (“Jaeger/Euro 13-pin”) connectors assign distinct pins and widely recognized colors for stop and indicators.

• ISO 1724 7-pin (“12N”)
  

  • Pin 1, Yellow: Left indicator (turn)
  • Pin 4, Green: Right indicator (turn)
  • Pin 6, Red: Stop/brake
  • Pin 3, White: Earth/ground
  • Pin 5, Brown: Tail/side (right)
  • Pin 7, Black: Tail/side (left)
  • Pin 2, Blue: Rear fog

• ISO 11446 13-pin (Jaeger)
  

  • 1L (Pin 1), Yellow: Left indicator
  • 4R (Pin 4), Green: Right indicator
  • 6 (Pin 6), Red: Stop/brake
  • 3 (Pin 3), White: Earth/ground (primary)
  • Additional pins handle tail, reverse, battery charge, etc.

Because ISO systems separate stop and turn circuits, the brake wire is red, while the indicators are yellow (left) and green (right). This differs from North American 4/5-way setups where stop and turn share the same left/right wires.

Passenger Vehicles: No Universal Colors Inside the Car

Unlike trailer connectors, passenger vehicle harness colors are not standardized across manufacturers or model years. Even within a brand, colors for brake-switch output and turn-signal circuits can change. The safest approach is to consult the factory wiring diagram or identify wires by function.

The steps below outline a safe way to identify brake and signal wires with basic tools.

1. Use documentation: Obtain the service manual or OEM wiring diagram for your exact year/make/model.
2. Test the brake wire: With ignition on, probe the brake-switch output; it should read 12V only when the pedal is pressed.
3. Find turn-signal wires: At the rear lamp or signal switch, probe for a wire that pulses 12V in sync with the left or right blinker.
4. Distinguish combined vs. separate systems: If the vehicle uses separate amber turn signals, the brake wire will be dedicated (often feeding the center high-mount stop lamp as well). If combined, the left/right rear lamp wires carry both turn and brake.
5. Confirm grounds: Verify a solid ground with continuity to chassis bare metal.

Testing is essential because aftermarket modifications, previous repairs, or regional variants can change colors and routing from any “typical” expectation.

Practical Notes and Caveats

Before you splice or connect, keep these practical considerations in mind to avoid miswiring or overloading circuits.

• Adapters matter: A vehicle with separate brake/turn circuits often needs a powered converter to feed a trailer with combined left/right stop-turn wires.
• Brake controller wire is blue on trailers: Don’t confuse the blue electric-brake controller output (7-way) with a reverse/lockout blue on some 5-flats.
• Aftermarket harnesses: Quality kits usually follow the standards above, but always check included schematics.
• Heavy-duty/commercial: SAE J560 (7-pin round) on tractors/trailers uses different pin assignments and is not the same as the RV-blade standard.

A quick function test with a multimeter or trailer light tester will confirm you’ve matched the correct wires and avoided cross-connections.

Summary

In North American light-duty trailer wiring, yellow is typically the left turn and brake wire, and green is the right turn and brake wire. In European/ISO trailer systems, red is the brake wire, with yellow for left indicator and green for right indicator. Inside passenger vehicles, wire colors are not universal—verify with a wiring diagram or testing to ensure you’ve identified the correct brake and signal conductors.

What color is the wire for a tail light?

The most common tail light wiring color codes, especially for trailers, are: White for the ground wire, Brown for the tail/running lights, Green for the right turn/brake light, and Yellow for the left turn/brake light. These colors may vary for other applications, such as for a vehicle’s specific tail light wiring, where wire functions are often different. Always consult the specific wiring diagram for your vehicle or trailer to ensure proper and safe connection.
 
Common Trailer Wiring Colors 

• White: Ground wire
• Brown: Tail/running lights
• Green: Right turn/brake light
• Yellow: Left turn/brake light

Other Trailer Wiring Colors (May vary by connector type) 

• Black: Battery hot lead
• Blue: Brake controller output
• Purple: Reverse lights or auxiliary 12V power

How to Identify Your Wiring

• Consult the Diagram: Opens in new tabThe best way to confirm wire colors is to find the wiring diagram for your specific vehicle or trailer. 
• Trace the Wires: Opens in new tabFollow the wire from the light to see what function it’s connected to, which will indicate the color’s purpose. 
• Check the Connector: Opens in new tabFor 7-pin connectors, you can look at the diagram or the pins themselves to determine the function. 

Important Considerations

• Vehicle vs. Trailer: Vehicle wire colors often differ from trailer wire colors. 
• Dual Bulb Systems: Trailers can have dual-bulb systems (where a single bulb handles both tail and brake functions) or single-bulb systems, which can change the wiring configuration. 
• Safety: Incorrect wiring can be dangerous. Always verify the colors and functions before making connections. 

What color wire is the brake and turn signal?

Goblin Guru

Function	Harness Wire Color
Turn Signal & Brake	Yellow / Dark Green
Park Light	Brown
Reverse	Light Green
Ground	Black

Feb 11, 2020

What color is electric brake wire?

The electric brake wire color for a trailer’s braking system is typically blue, and it carries the power signal from the brake controller to the trailer brakes. Other important wire colors are white for the ground wire, black for the 12-volt power supply from the vehicle’s battery, and red which connects to the vehicle’s brake light circuit.
 
This video explains the function of each wire in a brake controller setup: 54sU-Haul Trailer Hitches And TowingYouTube · Jun 15, 2021
Trailer Wire Color Code: 

• Blue: Electric Brake Output
• White: Ground (-)
• Black: 12-Volt Power (Battery)
• Red: Vehicle’s Brake Light Circuit (Stoplight Switch)

How the System Works:

1. Brake Pedal Activated: Opens in new tabWhen you press the brake pedal in your tow vehicle, the stoplight switch sends a signal to the brake controller. 
2. Signal to Trailer: Opens in new tabThe brake controller then sends power down the blue wire to the trailer. 
3. Brakes Engage: Opens in new tabThis power activates the electric brakes on the trailer, providing stopping force. 
4. Completing the Circuit: Opens in new tabThe white wire completes the electrical circuit, allowing the system to function. 

Important Considerations:

• 7-Way Connectors: The blue wire for electric brakes is present on the 7-way RV-style trailer plug, but not on the simpler 4-way flat plug. 
• Verification: Always use a multimeter to verify voltage on the correct wire when you press the brake pedal, ensuring proper connection and function. 
• Wire Gauge: Use the correct gauge wire to prevent damage and ensure efficient braking. 

What color wire goes with what color?

In standard North American AC wiring, wire colors should be connected by function: black (hot) to black, red (second hot) to red, white or gray (neutral) to white or gray, and green or bare copper (ground) to green or bare copper. For DC circuits, red typically indicates positive and black indicates negative. Always ensure you understand the specific wiring codes and applications, as mismatches can create hazards.
 
AC Wiring (North America)

• Hot Wires:
  • Black: The primary hot wire. 
  • Red: The secondary hot wire, used in 240-volt circuits or to link devices. 
  • Other Colors: Wires like blue are also used as hot wires in more complex systems, such as some 4-wire cables, according to this Reddit thread. 
• Neutral Wire:
  • White or Gray: This wire carries electricity back to the electrical panel to complete the circuit. 
• Ground Wires:
  • Green or Bare Copper: This wire is a safety feature that connects to the earth. 

DC Wiring 

• Red: Typically indicates the positive terminal.
• Black: Typically indicates the negative terminal.

Important Considerations

• Safety First: Opens in new tabNever connect wires of different colors unless the color codes clearly indicate they are meant to be connected for the specific application. 
• Application-Specific Codes: Opens in new tabWire color codes can vary depending on the application, such as off-grid systems or different types of appliances. 
• Multimeter Use: Opens in new tabA multimeter can be used to test continuity and verify wire functions before making connections. 
• White Wire as Hot: Opens in new tabIn some cases, a white wire can be repurposed as a hot wire for specific needs, but it should be marked with colored tape to indicate this change and ensure safety.