Here's a diagram of the Bargman plug.
As you can see;
Pin 1 is Ground
Pin 2 is Brakes (no power unless controller is active.)
Pin 3 is Tail lights (12 volts when lights are on)
Pin 4 is +12 Volts (12 volts from vehicle)
Pin 5 is Left Turn/Stop (+12 volts when brakes are on, intermittent when left turn signal is on)
Pin 6 is Right Turn Stop (+12 volts when brakes are on, intermittent when right turn signal is on)
Pin 7 is Backup Lights (12 volts when vehicle is in recverse) NOTE: (Also used for aux charging in some installations, and camera power in some installations.