You have to select the files as a playlist before starting. Also, I found that the microphone connector was "jammed shut" - I couldn't insert the jack all the way in and I was scared of pushing it any harder without breaking. It did however suddenly "seat" properly and then started working. So I would suggest you:

- check the continuity of your microphone is OK
- unscrew the microphone socket on the harness and check the contacts are free to move
- that the contacts have continuity to the contacts on the harness connector in the sled.