i bought a (supposedly) complete E53 tow hitch from an australian wrecker.the trailer plug harness (australian standard 7 pin round) goes to a capped 12 wire connector (only 10 plugs in it) that was clipped to the boot floor panel, just to the rear of the spare tyre. that connector has a single live wire with key on, but nothing else works, so there must be something missing. can anyone enlighten me what it is and where it fits??