So, these wires are all original, as can be seen by the wear on them, and the original solder joints. Since the disconnected lead can only reach a few pins, I think that it may belong on PIN #11. I've been suggested to try testing for continuity between PIN #11 and #12; no continuity is what we hope to find, as this should be connected to the Normally Closed (NC) terminal. Does this make sense?