removal of speedo cable from speedo in 74 Dart

H22A4 said

Might consider dropping the steering column (two nuts on the bottom side of dash and then either 2 or 3 bolts on the firewall where the column goes through) a couple of inches.
It’s tricky getting that plastic tab off without breaking it.

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Is the cable supposed to be free on both ends? In the past on other vehicles I've been able to remove without disconnecting at the speedo. Could mine just be stuck? The issue that started all this: at about 40 mph, the cable sounds like a mad rattlesnake and the needle jumps around so I have no clue as to speed.