I installed a Delco 12 CD changer in the trunk of my 96 Riviera this week. I have done this before on my Buick Roadmasters too. It is weird by all 4 of my Auroras (which I no longer own) had the harness already to accept the Delco changers. But for some reason I guess GM did not think Buick owners wanted a CD changer. As an aside many Cadillacs come with the harness too. Now this is even in cars that do not have a changer (none of my Auroras came with one).
So what I do is buy a slave harness and using the pin map in my Aurora/Riviera shop manual I wire it into the blue connector on the back of the radio. Now I had the Buick radios in my Roadmasters but they both started having intermittent problems with the single CD player either skipping or shutting off and on. This was the case with my Riviera too. So, in all 3 cars I swapped in an Oldsmobile radio. I prefer the layout, the sound and the functionality, plus none of them have ever failed me yet.