Yes the ACC line is easily available at the factory amp harness in the trunk or in the headunit harness. I was running a lot of wires anyway, so I took it from the HU harness.. It took running a wire all the way to the trunk, but like I said, i was doing it anyway... The good news about wiring up an OPUS in any BMW is that the battery is already there in the trunk so you don't have to run cables for the other wires more than a couple of feet
