Hi. My vehicle wire harness has a blue/white wire labeled "amp turn on". Mercedes E class. What would I connect this to on the N3 harness? I am not getting any sound out of the speakers, and I'm thinking it may be because this wire is not connected to anything.

that wire is for remote turn on or power ant. depending on application.

but more info on your vehicle is important. year? and so forth. you may need to rewire.

Sure, no problem. It is a 1994 Mercedes E320 coupe. I have a factory harness that has proper connections to hook up to the N3. I just have 3 wires from the car harness not connected to the N3 harness: a black ground, the power antenna, and "amp turn on". Thanks!