you tell what is what from the car harness by how it is connected to the factory radio and by using a multimeter thereby determining which lead is constant hot, which one is switching hot, which one is ground...the high output speaker connectors are all (+)
single connectors to each of four channels of the amp etc. The thin white lead which is connecting to ignition switching +12V hot powers the factory amp and power antenna buried in the rear glass defogger. The bigger question is does your Nakamichi actually wire to the factory harness. Some models are reported to only have low power out RCA connectors which is incompatible with the factory harness/powering through the factory amp. If this is the case, you need to purchase a separate post amp with RCA connector capability and circumvent the factory amp and wire to your speakers by building new cross-overs or eliminating some of the 10 separate speakers.
HTH,
George