Howdy!
I replaced the radio in my 1981 Thunderbird with a Kenwood about 5 years ago, or so. That Thunderbird also had an analog radio with an 8-track player. So I had the big knobs to pull off and the big rubber wiring harness coming out of the dashboard asd well.
I bought my Kenwood from Crutchfield
Crutchfield: Car Audio, Home Theater, Speakers, LCD TV, Plasma TV and they were incredibly helpful with everything. I got the wiring harness to mate with the big rubber connector coming out of the dashboard from them as well, so I didn't have to cut into the car's wiring.
In order to check the wiring, however, I went to an Auto Zone and got a Haynes manual, but before I bought it, I made sure it included wiring schematics in the back of the book. It'll show in that book the colors of all the wires going to each speaker.
I wish I could be of more help to ya more immediately, however my books are back home, and I'm off to college at the moment.
Good luck!
~Marcus