[G6Tanuki]

They're "Wander plugs".

Now alas extinct as a new-purchase, but a trawl of the usual online auction-sites will no doubt come up trumps.

The most-popular brand making these was 'Clix'.

In your case, try fitting something like a knife-blade into the gap between the two 'legs' of the plug-part, then unscrewing the plastic body. if you're lucky it will unscrew and then you can fit a new wire. If you're unlucky the plastic part will have become brittle with age and will crunble/split when you try to un-screw it.