I thought I would pass this on in case others run in to the same situation.
My console had been running wireless for a few days then I attempted to switch back to wired. After many failed attempts to force the console to re-sync (by holding down the + for 2 beeps) I then checked out the remote sensor batteries.
It had been a while since they were replaced, probably a good year or more, so I decided to swap them out. With a fresh set of batteries, the console was able to immediately re-sync in wired mode.
The old batteries were tested and showed about 1.0V rather than 1.5V for a AA. This might suggest that if you have weak batteries in the remote thermo, there is insufficient power to drive the serial lines back to the console and wired mode will not work.