Cannot really help, having not yet quite finished the grid, being stuck particulalry on 29a and 16d. I'm assuming that it will be something like ring the changes, spin the wheels, ...? I agree on the fruit machine bit as that's what my 4 unclued lights spell out. Will post again if I have any success!
Have completed it . You now have to juggle bits of words to get your BAR BAR BAR BAR across the middle line this will result in a well known book being seen in the top left hand corner and the author in the bottom right.