[dmack91]

I am going to be doing on in my 68 soon. If you are asking about adapting to the stock wiring harness - mine only has a power wire (goes to the fuse panel) and a green and black wire pair that go to the stock center dash speaker.

If yours is set up like this, the easiest way is to just start fresh. You can use the factory hot wire, and then run your speaker wires and ground wire fresh (you would need new multiple wires for any speakers anyway).

Stereos are fairly easy to wire in, and I usually find it easier to start from scratch than trying to figure out someone else's wiring system.