Try jumping a wire from the wiper motor case to the neg battery terminal.
If that works OK, you have lost ground through the windshield frame.
Are the bolts through the dash pad to the windshield frame clean and tight?
The only diagram I found was for a 78 (in tech), but it...
I've been offered a set of SOR springs a neighbor removed from his 76 because he said they were too stiff.
What are your opinions on the SOR springs? I currently have stock with add a leafs (sort of stiff in their own right)