Empty FuseBox Terminal

Here is factory schematics. 1st schematic shows DK blue wire and gray wire from tach. Look at 2nd schematic and dk blue wire(7th wire up bottom left) goes to fuse block.
Hope that helps.

View attachment 1715267645

View attachment 1715267646
That's NOT a factory diagram. I don't know where its taken from since mymopar never credits their sources, but probably Haynes, Motor or Mitchells.

Here's how to read one, as well as how to create a schematic.
Electrical Wiring (Session 247) from the Master Technician's Service Conference
or watch the accompanying filmstrip.
1968 Electrical Wiring from The Master Technician Service Conference Series (Session 247)

There's more if you want down in 1973
Master Technician Service Conference - Chrysler's Training for Mechanics