I have a 99 Bonneville, that came with the tape/equalizer stereo. A friend just gave me a JVC 12 disc cd changer. Does anyone know what else I'll need or how to install it? Thanks

If you have the factory stereo, it has no direct inputs for a CD changer. You will need what's called an "RF modulated" CD changer.

What accessories did your friend supply with the changer? Hopefully a long cable, a controller and a little silver (usually) box. If it is just the changer itself then you will have to find a JVC distributor and buy an FM modulator kit that will work with the model of the changer you have.