The 12 disc changer is probably the same type as the 12 disc Delco branded changer in my 98 Z28 which had the AM/FM/Cassette head unit (with AUX button). After I sold the Z28 I got an 01 Tahoe which had the AM/FM/with AUX button+remote cassette to which I added a 12 disc changer from
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(also using their Y-cable to allow keeping the remote cassette, just hit the AUX button on the head to switch between the remote cassette and add-on oem-style 12 disc changer) fully controllable ty the oem head. The new add-on changer used the exact same cartridges as the oem changer in the 98 Z28 but was branded Pioneer instead of Delco. I think a key to being able to add a changer is having that AUX button. BTW, with this setup you use the "5" key to switch cartridges in the changer.
Usually they run all the wires for everything, whether or not its
> compatible with an aftermarket changer.... Probably not. GM stuff is
> usually proprietary. I would be interested in knowing about this > also. I
> may own a 2000 or later Bonneville someday. :)
>
> >> A 12 CD tape deck installed in the trunk is an option. Does it come
>> with the wiring for it? If Yes, Is there an after market unit that
>> can be connected to it?