Hi, sorry for the confusing title.

Here is the situation. I have 2 lights in my downstairs, one at the top of the stairs and the other at the door. I would like to add a 3 light between the two lights so I have more light in the hallway. The thing is I have a access panel in the hallway but when I look in the access panel there is a bunch of electrical cables already there. I need a tool that will allow me to trace the electrical bus that the lights and switches are on. That way it will eliminate unnecessary cable cutting. Any help is greatly appreciated. Thank you.

You can get at a hardware store, a tone generator, that is a kit used for telephone work, however, YOU MUST shut off the wire you are testing. Connect the transmitter at one end, uses a battery in it for power, and you use a receiver that is a hand held wand that will beep when it detects the signal. These are fairly cheap, probably about $35-$40, made by Ideal Industries.

I use a toner out work all the time to trace out network and phone cables, duh! I didn't even thing to use it for electrical work. Nice thank you!