I reused as much original wiring, that was still good, when I replaced my harness with one from Painless. The dome light harness runs down the C-pillar on the drivers side and plugs into the rear harness in the trunk. At least in my 73 Barracuda.
If the wire is not brittle, I would not replace it. Just run the new harness to the dome light plug and terminate there. I think, as you rewire your car, you may see that the AAW harness does not have everything that your original harness has. Probably 85% will be new and 15% original, if useable, will be reused.
I reused as many plugs as possible, removed the old wires from them and added the new.