GMC SIERRA 2020 Owner's Manual page 303

302 Driving and Operating
Tail/Parking
Gray/Brown
Lamps
Reverse Lamps White/Green
Battery Feed Red/Green
Ground White
Electric Trailer
Blue
Brake
Heavy-Duty Trailer Wiring Harness
Package
If equipped, the trailer wiring
harness, with a 7-pin connector and
a 4-pin connector, is mounted on
the vehicle's rear bumper.
The trailer connectors contain the
following circuits.
1. Ground
2. Tail Lamps
3. Left Turn/Brake
4. Right Turn/Brake
1. Left Turn/Brake
2. Tail Lamps
3. Reverse Lamps
4. Battery Feed
5. Right Turn/Brake
6. Electric Brakes
7. Ground
If equipped, trailering camera
connectors are available in the
bumper trailer receptacle in place of
the four pin connector. The inside
trailer auxiliary camera should be
installed on the top left hand