I would love an answer on the speed wire as well. Another site I have searched on says it is in the original harness, only it is a gray/black wire but I am scared to hook it up and totally blow the system if that info is wrong. Also I have an aftermarket rear screen and it is connected with the RCA harness to the D3. Works great too! It even plays when the car is in motion and the brake isnt on. My next step is the bypass so it will play in the front too.