As built, the 317s had a button on the inner end of the some of the coaches. This was a rubber covered button of the same design (but only a single, not a double) as the door opening/closing ones next to the doors. Does anyone know what this was for? Edit: actually, I may be misremembering, it may have been the 319s. As built they had light up buttons, but the button in question was definitely rubber like the 317 ones.