Once upon a time I was flying a Shorts 3-60 (in the RHS) when the shaker came on and stayed on continuously.
We were descending IMC on an early morning freight flight into BEB.
I may as well add that this a/c had no auto-anything or even a flight director. We were going fast for us, at least we thought we were (!) but why the shaker?
Had to hand fly it for about 10 mins like that by which time I don't know which was shakier, me or the plane.
Fixed it by (the Capt.) pulling the CB.
Just to say, these things are not infallible.