threaded opening between Cummins and Allyson Transmission

Thanks for the response. The opening is about the size of a quarter and threaded with no metal door cover, so I will check into a plug that must be missing. I will check where the fridge plugs in for 120 VAC. It cools very nicely, but like last night, just stops a/c and goes to LP. I did notice that the socket that it plugs into has two spots available. Does it make a difference which one I plug into?