[soundman98]

to my knowledge, no vehicle-side wiring from any mfg is EIA compliant.

that's part of the reason to use the adapter harness with a standardized color code and labels(when installing an aftermarket stereo, the aftermarket stereo colors will line up), though the best reason is to maintain the oem plugs to allow easy conversions/adaptations later, and use the adapter as a sacrificial wire loom--it's cheap and easy to aquire should something need to be changed later.

yes, as per previous outlines, the toyota speaker adapter harness will connect into the amp harness. but the significant difference is that the 'front speaker' terminals serve as the 'input from radio', and the 'rear speaker' terminals serve as the 'output to door speakers'

forewarning, there's no way to maintain front/rear fader capability using this method.