Quote:
but which wires on the head unit will need to be connected to the harness adapter and which shouldn't be?


If you know which wires do what, that question will answer itself. If you don't know which wires do what, it's time to have a pro installer do it for you. You can let out the expensive blue smoke if you start hooking up wires willy nilly.

Essentially, both units need constant power, switched power, and ground. Then you need to choose which of the two units is going to be responsible for making the amp-remote line go high. That's the one whose amp-remote line gets connected to the amp.

Regarding the RCA cable inputs and outputs, that's covered here and here.
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Tony Fabris