Looking for 70 dart swinger rally harness
I haven't needed to do it for myself. I've helped others doing the same.
If you compare the wiring diagrams you'll see very little difference in how the instriment panel is wired. Added wire, later model wiper circuits, interior lamps, etc.. are a different issue but nothing that cant be sorted.
To put a 67 to 69 rallye harness in a 70 or later is much more difficult.