Sorry, I don't exactly remember the pin arrangements, though I recall studying them to make sure they lined up. With fuzzy recollection I thin there were 3 pins in one connector and 5 in the other - but I could be wrong.
If I recall correctly, the two connector ends on the Y are shaped different to assure that the correct connector is inserted, i.e. the cables are "shape coded". When pressed firmly enough I recall they kind of snapped together so they wouldn't come apart easily. You'll know if you have the connector inserted fully when it snaps together.