99 chevy s10 mp3 input project

Am working to find out some information on the stock Delco radio
installed in my 99 Chevy S-10. AM/FM/CD player head unit, and am
trying to add in an aux input so I can plug in my MP3 player. Have
searched online, and am not willing to shell out the 70+$ for some of
the products on the market. Would love to be able to take advantage of
the 9-pin connector on the back of the radio that's used ot interface
with some of the aux components for the radio itself. Does anyone know
the details of the pinout for the connector, or of a similar project
that's in the works/has been completed?

Thanks,

Mac