!!!!! W A R N I N G !!!!!
When I made a remote dongle for a competition clock, I asked IFI if i t would be correct to connect the port in a similar fashion, and was warned not to use 12 as ground, as it was to be reserved for some future use. IFI said the 2002 manual had not been updated before publishing, in this content area.
I posted this last year, too.