Rear speaker not working

I've got a 2002 GMC Envoy and the rear driver's side speaker just stopped working a couple of weeks ago. I checked the speaker itself and it does work, but when I connect it back up to the wire in the vehicle, it doesn't work. All the other speakers work just fine and I have no problems with the head unit. Any and all idea as to what this could be would be greatly appreciated.Ariel