Interesting.
This seems to act like READY, but it is doing READY for drive B as well. In other words, CP/M can't detect a missing disk in Drive B with this mod in place when a disk is also in A:.
That white ribbon cable goes to the drive motor. Not sure what I have connected Pin 34 of the floppy connector to.
There are other pins that act like RDY on the controller chip, but they all stop the boot process: after the boot track and EMT file have loaded I get a blank screen, then when I disconnect Pin 34, it continues, but halts with "drive not ready".