Hello there--
I have two exterior 110 outlets [with weather-tight boxes] recessed in the stucco wall on rear wall of my home.
They are fed by one circuit that doesn't seem to have anything else on it--and I believe the circuit is GFI protected [home built in PA in 1976.]

How do I run a line from one of those receptical boxes to a new box out on the patio?

Much obliged for your help!
John

You can get a weatherproof extension ring for one of the exterior outlets, see photo of one I included. This will give you a method of accessing one of the outdoor outlets, and then either EMT conduit with raintite compression fittings or PVC conduit can be installed on the surface to the patio outlet.

Best to be sure all the exterior outlets are GFI protected somehow, either with a circuit breaker, (expensive, about $30-$40), or a GFI receptacle (about $10.00).