The author provides a wiring scheme for the iPod connector or cable, specifically for the iPod Shuffle (2G) USB interface. They state that according to reports, the pinout should be correct. The author also notes that the headphone jack on the iPod Shuffle also functions as a converter from audio to USB data. They highlight the presence of a diode between the VCC and GND for perfect isolation of VCC. The author advises that when charging is needed from something other than the stock base, pin 3 should be grounded and pins 1, 2, and 4 should receive Vcc.
https://pinoutguide.com/PortableDevices/ipod_shuffle_pinout.shtml