i finished installing a 90BT in a jeep (jk) 2007 with premium factory sound package. i used the PAC wire harness for factory upgrade systems (i.e. self amplified systems). in doing so you will see that the rear speaker outputs are the wire that feed the amp, hence sound prompts comming from the front wires will not be heard. With the 90bt the nav voice command, bluetooth, and clicks when touching the screen are supplied through the front speaker output wires, which do not go thru the amp. having said that i took the front out wires from the pioneer 90BT unit and connected them to the rear wires of the wire harness (of the corresponding side of-course).
to clarify i took the left front positive wire from the 90BT and connected it to the left rear positive wire from the PAC wire harness. seems weird but it worked perfectly.
i can only speak for jk wranglers.
chris
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2007 Jeep JK
Pioneer Premier 90BT