The black connector in the last pic is actually what lets the DIC communicate with the radio to store the date and produce the warning chimes. The wiring harness you have will probably work (if we knew what it was/looked like), you just won't have the date available on the DIC, nor will you have warning chimes for any messages that show up on the DIC.
And that box looks like an XM radio FM transmitter, which might explain the other wire you found in hanging from the rear deck (second pic). Probably wires for an XM antenna?
