Series 1 started with a centre horn button and wires down a hollow steering column. Later Series 1 had a solid column and the button on an arm clamped to the steering column. This continued on through Series 2 and 2a, but was scrapped later as you describe the button went back onto the steering column - the parts book does not give a changeover date or a chassis suffix, but lists them as alternatives. I suspect the side horn button may have continued longer on Australian built vehicles. As far as I know, all from suffix 'C' used the centre push with the new steering wheel, and this was kept unchanged for S3.

