I might be on to something here.  I read in the archive that the switch 
also tells the side mirrors to heat up.

Well, last spring the passenger side mirror was assaulted by a tree.  It 
was amputated at the wires, and later reattached, BUT WITHOUT THE WIRES!

So, is it reasonable for me to expect the rear defrost to reanimate upon 
splicing the wires back together?

Thanks again,

Chris Wyatt
'87 Syncro GL
Fairbanks, Alaska