65 dart signal switch harness?

The orange wire runs alongside the turn signal switch wires but isn't one of them. It is for the shift indicator light as already mentioned.

The wires on the new switch aren't exactly the same colours as the wires on the old switch, but if you use a bright light and a careful eye you'll see they're close enough to the same to avoid confusion: there is a lighter green and a darker green. There is a lighter brown and a darker brown. There's a red, a white, and a black. Just put the new wires in the nylon connector housing in the same location as the old wires, one by one, colour by colour, as described here. The orange wire stays put; you won't be replacing it.