The cable on my stitch regulator acts up every once in a while so that it appears to be plugged all the way in but it's just plugged in enough for the manual switch to sense it so it won't let me operate manually but not enough for the stitch regulator to kick in. I can tell when I need to fuss with the cable because it doesn't "hum". I usually unplug the cable going into the stitch regulator & plug it back in then turn it just a little until I hear the hum. I have a Voyager--not a Tin Lizzie--but the symptoms you described sounded just like what my Voyager does.