I'm not a wiring guy. I can run a test light and make things work with a new wire (usually). @Mattax and @halifaxhops are the experts. Chris not so much! LOL
Not sure what I can offer.
Sold my '74 Nova when I moved here.
Talk about a great car to learn on. Super simple and great access to everything.
Only electric problem it ever had was a taillight ground to rust.
I assume '72 Blazer is basically the same electrics in a bigger vehicle.