have a 2006 X5 with an aftermarket class A hitch and I can't seem to find the wiring harness. have looked under and see nothing. in the spare tire compartment I see something that might be what i'm looking for. it's a black square receiver but looking nothing like any towing wiring assembly that i've seen. will try to get a pic but in the mean time if anyone has an idea or suggestion, it would be appreciated. thanks