In message .com,
Boltar writes

I've no idea how its actually done but couldn't they just be connected
with seperate cables (instead of via the coupler), which twist in the
middle
so
to match up with the other unit?

eg:
The problem arises that in service, if a train brakes down and needs
assistance from the rear then a mechanical coupling cannot be made by
the end with the sprung buffer to another of the same. (I forget whether
this is A or D end.
--
Clive Coleman.