Checking Trailer Socket

Courtesy of VOLVO CARS CORPORATION

7-pin connection 

1. Brake lights/Left turn signal
2. Ground
3. Spare (Brake lights, Electric brake)
4. Brake lights/Right turn signal
5. Charging
6. Running lights
7. Spare (Back-up light)

The cable for pin 3 for 7-pin connection is blue (BL). It is taped on the cable harness approx. 1 meter from the trailer socket.

4-pin connection 

1. Brake lights/Right turn signal
2. Brake lights/Left turn signal
3. Running lights
4. Ground