Without a long drawn out explanation, just visit the web page I created on this project:
My wiring project

 

You'll have to to determine the type of box that the switch is mounted on and if there is a 2-wire "feed-in" cable in the box.It's possible the only 2-wire cable in the switch-box is a "switch-loop" from the ceiling box-the Black/White wires on the switch indicates such a connection,which means you don't have 110 volts for operating the sconce. If the box is a single-gang plastic "gem" box then only one device can be mounted on the box.----Good Luck!!

 

oamaro:

Compliments on your web page. Very nice work.

PATTBAA is right. Your source of power is probably at the light/fan fixture. You're going to have to get power to your switch location.

What's above the ceiling in the parlor? How about under the parlor? Unless you've got access above or below that room, I'm afraid you're in for some work.

You could leave the light/fan wired as it is. Remove its switch box (it looks like an old work box) and replace it with a double.

Run 12-2 from a source of power to the new switch and from there 12-2 to the sconce.
At the switch:
Power black to either screw on switch
Power white and fixture white nutted together.
Grounds (bare) nutted together and to the green screw on switch.
Fixture black to other screw of switch.

At the sconce:
White to white, black to black, bare to body of fixture.

 

Thanks AbNORMal! I'm a better graphics/web designer than electrician..unfortunately.

As far as access top and bottom, not a problem. It's a (well-built) 1912 Craftsman home and there is a fairly large attic area (I can stoop in it) and enough bottom crawlspace for sitting up in (it has a "California basement" as it's called in these parts). I will go up there tonight and take some photos of what I find (!).

As a non-electrican though, what is "12-2"? (gauge??

 

Yes it's 12 gauge, 2 wire. The ground isn't counted but it's there.

Sounds like you can get power from the crawlspace. Is there an outlet there you can tap into? If there's one, make sure it isn't in a circuit which is maxed out.

 

I climbed up into the attic tonight and took some more pictures. If you click on the link under "And what did I find in the attic??.." at the bottom of the page, it takes you to those pictures.

I'm not sure I liked what I found.

 

Well, what you found in your attic isn't unusual, even tho' it ain't pretty.

You may or may not find a box over the fan. Since this was done by a licensed electrician, I'm betting there's one there. Can you drop the fan housing and check from the parlor?

The "attic spider" looks pretty maxed. Where's your panel? You might want to do everything from below on a new feed.