ultimately, its easy as cake. You said the sconces now have pull-chains? that means that there is power in the boxes. If one box has 2 pieces of wire, and the other 1 piece, and im assuming it is steel jacked BX by your old plumbing pics, all you need to do is run a wire from the box with 2 wires going into it, over to the new switch box, hook a switch up, white to the top, black to the bottom, ground to green, and swap a couple wirenuts around in the sconce's box. Totally doable for a novice.
Only fun part would be if it is old BX, they didnt often use wirenuts, just tar and nastz *** tape to make connections. Its great fun getting them apart. Need to make sure the wires insulation, probably think cloth, is not shot and falling off.
Pics would be great, i could draw the instructions right on it for you if it is what i think.
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