JR, The relay you are showing is not for a rear window defrost . Looks more like a old H/L dimmer relay. I had to go find my old factory parts book to find the correct relay parts #.  
   The part # is 111-963-141B.  It should be a cube shape( about 1 inch square) and has a screw mount tab and only two connectors. Hope this helped

This one is mounted exactly where you noted.  My problem is I have one wire, which is fused, that connects from the regulator and I believe to this relay.  I have looked at wiring diagrams but still not sure where to connect it.  I do believe that this wire goes to the relay but can't be 100% sure.  If it does not connect to this relay, then I have no clue where to connect it to.  Maybe if I state where it comes from on the regulator, that would help.  I will have to check tomorrow evening.  Thanks!