2003 Lexus LS430, Pre-Amp Audio Signal

Hello, I'm working on a 2003 Lexus ls430 with navigation and ml sound. I'm looking for the pre-amp audio signal wire(wire harness from nav screen to the ml amp) thanks, tim

Do you have an old computer speaker you can sacrifice? If so, cut the 1/8 inch plug off and strip the end of the cable back a few inches. Separate the shield from the 2 center conductors, ground the shield to the case of the amplifier or radio, with the radio turned up a bit touch the center conductor to the plugs with the smaller wires. You will find 4 wires with audio on them. On the amplifier there are several plugs, I am pretty sure it is the plug with the most smaller gauge wires. Of course it needs to be an amplified setup. You will have to power it. Once you find the 4 wires with audio, you may be able to use balance and fade to determine which wire is which channel. Thinking back this system may have a digital balance and fade that is done internally of the amplifier. But you can find the audio.