2001 Buick Century Oil leak on wiring under car

I noticed something I thought was a plastic bag hanging down under the engine. I reached under and pulled on it and found it was the insullation to some wiring harness that was oil soaked and came apart! The olny thing I can figure is when having my oil changed and filter changed at Wal-Mart numerous
times, they let the oil run down onto the wiring.
I couldn't get under the car to see where the oil drain plug is located, or the filter location since I don't have a jack to lift it high enough to see.
What is this wiring and where does it go too?
My car has never leaked oil before, and still doesnt.