WTB: S4 Spider OEM Radio (for 91-94).
Argh. I will find one!!!They are different (no touch screen controls on the S4 head unit).
On the S4 it is Fujitsu system (head unit and CD changer), both of which are near impossible to find. If you do have the OEM unit and it is not working, it can be repaired (I looked into this before I discovered it was a $1 fuse causing the changer not to work).