Still looking for brake lights and turn signals... HELP!

I'm not sure on A bodies, but B and E bodies with 4spds did have linkage to the column in 1970 as you had to put the car in reverse to get the key out. I would start isolating some wires, check the harness(all of them) to see if they have rubbed through somewhere, been piched, aftermarket accessory wired in, etc.