My guess is that it's a circuit for lighting, and the reason that it's a loop is the wire comes out from the stucco and then heads back in to go to the next light. It's quicker to do it this way then to cut the wire.
If I'm correct, there is a switch somewhere that energizes this circuit. If you can get a non-contact voltage detector, you can use that to verify which switch is hooked up to the circuit. Once you know that, it's simple to turn off that circuit and then put up fixtures. They would mount directly to the stucco.