Quote:
whether this pin is used on the IDE cable, or whether I'm chasing a red herring by attempting to repair the missing copper


Found a description of signals on the 44 pin IDE here (page 15). Don't know if that is always the same (ie all signals always used, or if this description is exhaustive or not)... but might be useful.

From your description it sounds like it's one of the corner pins that isn't connected (ie 1, 22, 23 or 44, depending of the orientation, which I don't recall)

Pin 1 is described as RESET, 22 as GND, 23 as IOW-/STOP and 44 as Not connected.
So it could be that it is correct for it to not be connected...

HTH,
_________________________
/Michael