Unknown plug connector on 05 GMC Safari

I found a lone plug connector, unattached to anything, while removing the paneling from my van. Would anyone happen to know what it is for? It was located on the drivers side rear wheel well. Here is a photo:
Details on the van: 05 GMC Safari, passenger model, has rear heat and AC if that has anything to do with it.
Details on the van: 05 GMC Safari, passenger model, has rear heat and AC if that has anything to do with it.