Trailer · 7-pin · lights and ground
7-pin trailer wiring diagram: connector, lights and ground
A trailer connector carries every rear light function plus a ground. “7-pin” means different plugs in different regions, so first check which standard your vehicle and trailer use; then each pin has a fixed job.
Open the editor · ▶ Run the live demo
US 7-way RV blade (SAE J2863)
| Pin | Function | Usual colour |
|---|---|---|
| 1 | Ground | White |
| 2 | Electric brakes | Blue |
| 3 | Tail and running lights | Green |
| 4 | 12 V auxiliary / battery charge | Black |
| 5 | Left turn and stop | Red |
| 6 | Right turn and stop | Brown |
| 7 (centre) | Reverse lights | Yellow or purple |
European 7-pin (ISO 1724)
| Pin | Code | Function | Usual colour |
|---|---|---|---|
| 1 | L | Left indicator | Yellow |
| 2 | 54G | Rear fog light | Blue |
| 3 | 31 | Ground | White |
| 4 | R | Right indicator | Green |
| 5 | 58R | Right tail light and number plate | Brown |
| 6 | 54 | Stop lights | Red |
| 7 | 58L | Left tail light | Black |
Diagnosing trailer light faults
- Several lights dim or glowing when another is on: almost always the ground — check pin 1 (US) or pin 3 (EU) and the trailer’s ground wire to its frame.
- One function dead on both sides: the car side — fuse, trailer module or relay for that function.
- One lamp dead: bulb, its holder or its wire on the trailer.
- Modern cars may need a trailer module so the car’s bulb monitoring and LED lights work with the trailer.
Draw the trailer circuit in WireForge
- Add a Battery, fuses and Turn Signal, Brake Light and Tail Light devices for the trailer.
- Use a Negative distributor as the trailer ground: every lamp returns through one wire to the car, like the connector’s ground pin.
- Give that ground wire its real length and cross-section and simulate with all lights on.
- Click the ground wire to see the current of all lamps together and the voltage it loses — the reason trailer lights go dim.
Questions
Why do my trailer indicators flash fast?
The car thinks a bulb is out — usually because the trailer lamps are LED and draw too little, or the ground is poor. A trailer module or load resistors fix it.
What wire size for a trailer harness?
For lighting 1–1.5 mm² is common; the ground wire carries the current of all lamps and should be at least as thick as the thickest feed. Brake and charge lines need more.
Is 13-pin better than 7-pin?
In Europe the 13-pin plug (ISO 11446) adds reverse light, permanent power and caravan circuits, with separate grounds. Adapters exist in both directions.