The empeg ISO adapter only contains wires for power, ignition, remote turn-on, etc. There are no audio cables in that adapter.

In order to get sound out of it, you need to connect the audio cables (the red/black pairs labeled FRONT and REAR) to an amplifier. I don't know about connecting line-level plugs to the factory BMW amplifier, you might need yet another special adapter to do that. I don't know what the BMW amp is like.

The other option is to use an amplifier of your own, skipping the factory amp completely.

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Tony Fabris