Universal CD-CHANGER controller

[Predator_MF]

There are a lot of people that want me build an Universal CD-changer controller (a board that could make possible connection between any CD-changer and any Car-Radio that has a controller for CD-changer). I have expirience with PIC controllers, so it won't be that hard, except I do not have enough info for the interfaces that are used in some radios...
Can somebody help me a bit, if I build it it will be opened source and I'll give it free!