It is possibly a bit too young to be a series 2 part.
I have a couple of series 2 parts catalogues and it isn't in either of them.
It is probably military given the specification of the connectors, I have never seen such waterproof connectors on a civilian spec vehicle, or on later model military come to that.
It is from that era when the military went to manufacturers with a specification and asked them to build it.
The part number was on the packaging and on the cable itself, unfortunately the description on the packaging was illegible.
I'm just curious what its original function was, mostly because of the twin connector fitted at one end, not a double connector but a twin. One port of which has a filler plug in it thus making it a dead end.