I'm stashing this here in case I need it again in the future, but it may be useful to other folks as well.
If you ever need to integrate SeaTalk
from an AutoHelm
ST50, or any other models that use the little round connectors with 3 pins, the correct female connector is a Switchcraft 16282-3SG-311, which can be purchased from Digi-Key as SC1205-ND.
The connector is a real bear to solder onto the wires, and it would have been quite a bit easier and $13 cheaper just to cut the connector off my ST50, although it was nice to not bucher the hard-wired factory wiring
Anyway, storing it here for anyone else... Or me later!