I have the rear window and related harness form the 74' and plan to instal that in the 75'  The wiring for this is not in the 75' at all so this is a true retrofit like the fog-lights.

 

Parts needed:

 Rear defrost window

 Wire harness

 Dash switch

 

The wiring harness will connect to this post on in the lower dash fuse block.  This is the before picture of the entire fuse block that was removed and dipped in Vinegar+Salt and then rinsed and polished with Brasso and a toothbrush: