When it's not ringing. Depending on your distance from the last repeater, the voltage may be as high as 200 volts AC when ringing, so be careful. It's a current loop, so the voltage can vary quite a bit, but it's nominally 128 volts centered about the more negative one of the two (tip and ring) wires, here at my house. Yours may differ. I have a specification somewhere ...

If you figure out which of them is more negative, and use that position in the various junction boxes, you'll be just fine. BTW, don't hook up your phones in a "star" or parallel configuration. put all the (RJ11) sockets in a chain configuration. You'll get cleaner signaling. The phone doesn't know what those colors are, or what they mean, and neither do I, though I've read that, for a two-line system, you use black and yellow for the second line. Since I can't tell the red from the green, I don't know which is tip and which is ring.

RE