Hi Dave,
This is the pinout for that connector:
3-pin Connector DEC:
Nr 1 Plus 0-12 V 5 A max for fan regulation through AS
Nr 3 Minus
The connector itself is a threaded Lumberg 3p DIN connector
SV30 Lumberg, DIN Audio / Video Connector, 3 Contacts, Plug | Farnell
Regards,
Waldemar