Plan B, ditch the wire I suspected was surplus to requirements - there's like 0.3ohms between one of the contacts on the A junction button and the black wire in the the Di2 loom, and whaddayaknow, that's the go. So here's a far less hair-tearing headphone socket from the same pillaged phone.
Also shown is the section of glue gun nozzle I carved up to serve as a mount for the PCB and light pipe for the LEDs. PCB hotglued into it
And here we've got my $40 wing and a prayer Aeronova ripoff with a 2mm hole in it. After considering it, I decided to put the hole as low as I could, which seemed to make a lot of sense.
