I'll say this, you've got the most messed up wiring. '67 harness, '70 turn signal switch, 72+ wiper motor, '71- wiper switch, and now a thermal flasher relay...
Switched power --> flasher relay 49
flasher relay 49a --> signal stalk center terminal (the one you had your screwdriver on in that picture from your other thread, yes probably black)
flasher relay 31 --> ground
You also run another wire for the flasher bulb in the speedo:
flasher relay 49a --> speedo bulb
Actually, what type of relay do you have, how many terminals, and what are its terminal markings?
An XL flasher:
switched power --> flasher +
flasher L --> signal stalk center terminal
flasher L --> speedo bulb
A PXL flasher
switched power --> flasher +
flasher P --> do not connect
flasher L --> signal stalk center terminal
flasher L --> speedo bulb
A KXL flasher:
switched power --> flasher +
flasher L --> signal stalk center terminal
flasher K or KBL --> speedo bulb
Might also be an S label, but S=L=49a