Pin 2 on each connector is for Turn/Brake, to Brown on the light.
Passenger = Blue/White
Driver = Blue/Violet

Pin 3 4 White is feedback signal to the BCM
Pin 4 3 Black is ground.

Not for a trailer connection, but I did tap into pin 2 for each side's turn/brake signal..
My RH passenger side with a Tee harness tapping the Turn/Brake signal.

Source: https://www.chevybolt.org/threads/bolt-euv-2023-break-light-wire-color.57143/