black is probably Ground - you can measure it via Ohm meter - 12 USD
RED/Black is def power via the fuse block - same here measure it -
I had also 2 wires hanging out of the "master wire loom" although the radio was hooked up via a separate 2 wires.
per the nice wire docu (tech notes) the BR goes to the AC blower switch comming from fuse 10