'This is the locking mechanism for the end sleeves that you insert into the outer sheath from the other side. (Remember the rubber plugs that seal the cable to the outer sheath, making it waterproof.)'
Left side: pins for female connectors; right side: pins for male connectors.
On the right side, you need to slide the purple slider against the housing wall. Only after the pins are locked can you properly push the housing halves together.
In the right connector (image), the purple fuse holder has two strands that extend forward; press these strands to the left against the black housing wall.