I added a 4-pin trailer harness for about $90 it works perfectly ok and I keep it in the left storage area when not towing. You should check if PO did the same.

I discovered when installing the wire taps for the aftermarket wiring that the PO had installed but removed the identical type of wiring kit (the wire taps were still on the wires)

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)