There are small strips of that metal tube (maybe only one, maybe two) that act as "arrowhead" anchors to keep the tube from pushing backwards --and out-- as you connect that plug to its mate. When that type of plug is first built, those strips pop outward to lock the metal inside the plastic housing as the tubes (plus their wires) are pushed into place.
You'll have to find a suitable tube, preferably metal, that JUST fits over the plug's tube, and push down over it to collapse those two arrow-things. Once that's done the plug's tube will pull out the back. Sometime a metal ball-point pen tube will work, but a hobby-shop piece of 1/8" brass tubing works quite well. Standard "Molex"-style wiring.
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