Well guess what.
It works! ��
Thanks to Simon (
SD1too) and Ray (
raykay), we narrowed it down to the two Green/Orange and Green/Purple SWC wires looking like they should be connected to the missing pins 10 & 17 in the new BMW adapter connector. I did try that a couple of days ago but didn't work. Having reflected though, I considered I may either have connected them just one way round and not tried the second permutation, or perhaps the wires hadn't been pushed in firmly enough through the back of the connector into the blank hole where the male pins on the radio lurked.
I set about it more scientifically this afternoon trying both permutations and making sure the connections were firm, and - all SWCs now work.
I'm all made up.
So for anyone wanting to install a Harmony with the BMW connector into a car with a VDO CD413X and ISO connectors, the SWC wires (as discussed above) are G/O and G/P connected to the small green ISO connector which must be cut off - or perhaps use a male mini-ISO adapter to plug into the green connector to preserve it - and the two wires extended. The G/O wire goes to pin 10 on the BMW connector and the G/P wire goes to pin 17. They must be that way round. Those positions are blank holes and have no female pins installed, so you need to address that. I used a small round 3mm plastic rod, cut two pieces so each pushed down inside each hole but still protruding about 4mm so they can be removed, which tightly held the wires in contact with the male pins 10 and 17 on the radio. I'm sure I could have sourced the correct female pins in time but I'm happy on this occasion to bodge it as it's secure and safe.
If you have other permutations of radios to fit or swap, have a look at
https://www.the75andztclub.co.uk/for...d.php?t=214040 which is a similar thread with raykay's input for the other radios. 8-year old thread, still relevant.
Thanks again to everyone who contributed. The forum rocks.