Figured I'd post these after forum search for the factory aux plug yielded conflicting results. Mine's a 2023 1250. Perspective here is looking at left fork tube opening from the ignition switch. The plug is zip tied to a "L" shaped bracket and has a deadhead plug in it.
Sprung for the $17 male pigtail from BMW since harness splices are a flag for me when shopping for used. The pigtail has 3 identical yellows numbered 1,2, and 3. 1 is negative, 3 is switched positive, and pretty sure 2 is CANbus from wonder wheel.