I doubt very seriously if those are trace wires. Code requires an AWG # 18 "Yellow" trace wire when installing plastic "Gas" lines but there is no requirement for a trace line for water lines, not meaning to say that you can't install a trace line with water, but it is almost never done. I would consider using a crimp on Butt splice to connect the wire, then cover it liberally with Scotch 33 live rubber "Splicing Compound" tape. The Splicing compound tape is a thick live rubber tape that has a thin plastic membrane separating the layers on the roll. As the tape is applied the membrane is removed and the tape should be stretched and wrapped about three layers thick. The tape should be stretched to about twice its length during installation and wrap about 3 to 4 layers. The tape will quickly shrink back to its original size. As the tape shrinks back to its normal size the individual layers will compress into what appears to be a thick solid layer of rubber. After the splicing compound tape is applied it should be topped with a layer of vinyl electrical tape.

Thanks brickeye - I guess I don't understand what chance I could be taking. Where could those wires possibly have come from? My parents bought our home (the model home in our neighborhood) from the builder a few months before I was born. My family has been its only inhabitants. My mother did one renovation when she moved the laundry to the basement (sort of wish she hadn't done that), and the wires were capped and sealed into the box. They're the builders wires for the 120V outlet in the original laundry area. Is the concern that the wires could have been incorrectly installed when the house was built? I removed the plywood, uncapped the wires, read the voltage (120V) and connected them to a 15A outlet, wrapped it in electrical tape and screwed the outlet into the box. Here's a "before" image. The purple wire was live, the white neutral. I appreciate your input. I have plenty left to learn and don't want to destroy the house.

Sometimes electricians carry the 3-wire from one switch to the other via the light's box, to make a shorter run or just because it's convenient to route that way. If that's the case, then there should be a grand total of eight wires (excluding grounds) entering the light box: * 2 hots (one black, one some other color) and a neutral (white) from the first switch. * 2 hots (one black, one some other color) and a neutral (white) from the second switch. * A hot and a return (not a neutral) from the second switch. One of these should be black and one should be some other color. However, if the circuit is romex, one of them will probably be white; if so, it should be painted black or have black tape on it near the end. These would be the two wires connected to the light fixture. What it sounds like to me is that the light box is not really "between" the two switches in terms of how the circuit is routed, even though it may be physically in between. My guess is that the yellow is the switched hot, and the white and green are what you expect. I'm not sure what the always-hot black is doing there. Possibly at some time in the past, there was a ceiling fan installed there with a light, and the yellow was connected to the light lead of the fan so the light could be switched on and off with the wall switches. The black might have been connected to the motor lead, and the fan turned on and off via its own pull chain. That's kind of unorthodox, but in an older installation, it wouldn't surprise me.

Where is the light fixture in this scheme? How is the second switch wired? Where is the incoming power wired in? Is this the end of the branch circuit or does the power feed through to other devices? Might it be a four-way setup? There are several variations on how to connect a three-way light so you need to know how the other elements are connected. I recommend that you study a book on basic residential wiring. There should be several at your local library or you can find them at home Depot, Lowes, etal. Your web browser should also be able to find a few illustrated explanations.