Here’s the illustration from the documentation:
Based on that the audio/PTT cable will look like this:
MIC 3.5mm TRS tip (MIC) → 3.5mm TRRS ring 1 (RIG_AFIN)
MIC 3.5mm TRS ring (PTT) → 3.5mm TRRS ring 2 (PTT)
MIC 3.5mm TRS sleeve (GND) → 3.5mm TRRS sleeve (GND)
PHONE 3.5mm tip (PHONE) → 3.5mm TRRS tip (RIG_AFOUT)
PHONE 3.5mm sleeve (GND) → 3.5mm TRRS sleeve (GND)
This appear to line up with the audio cable from Elecraft KX kit:
Please report any build/test results.
Manual: Youkits_SK-1A_user_2017.pdf (320.1 KB)