When was the 4 terminal set changed? All of my Cruise Commanders as well as AC and DC Commanders use the same type of connector on both ends.
Not sure turning it upside down will open up the contacts but a small jewelers screwdriver will.
Necrails, remove the wire next to the one that isn't clamping down and observe the difference between the one that clamps and the one that doesn't. It should be obvious what the problem is assuming the connector is not defective.