I realized that I used an incorrect term in the subject line of this thread - it's really about the air vent control, not heater levers.
Thanks to the fine guidance here, today I saw that the wire had come free from the lever and I managed to reconnect the wire to the upper right lever blindly, by feel through the dash speaker opening, into the slot under the castle nut and tightened it down. Thanks for your help and photos on that!
Now the next problem, the linkage is very tight and the lever won't span the full range. I cannot find in the Tech Manual - where does the other end of the upper right lever connect to the vent control? I have a feeling it goes under the dash? Any photos, please? I've got a nice fat Frigiking AC sitting under there!
Thanks