[elfer]

I think we do know what all the wires do. The car wires are all documented in the BMW WDS linked above - ask if you need help deciphering that - and the radio connectors appear to be international standard - Google ISO10487. All you have to do is match them up.

As I say, ask away for help with WDS. The colour codes there are German language abbreviations for colours and the wire diameters are in mm, but we have the knowledge

 

[elfer]

Solderers will often say soldering is better. Crimpers will often say crimping is better. Truth is, either done properly is better than the other done poorly. FWIW, BMW generally crimped rather than soldered their wires to their terminals.