Originally posted by Smolenski7:
However, there are 2, 4 conductor cables going into the house from the left side of the box (the side I DO have access to).
If you have a 4 pair cable going to your modem you won't have a yellow/black.
Whatever color is currently feeding things are feeding the phone's and probably the modem too. I have no idea how it was originally filtered or wired. The drawing Merritt supplied is what you want to follow. You'll have to see what pairs are currently in use. Again I think you're over your head. From your post you don't seem to be grasping what you're being told. If I were you I'd check the phone book or online for a phone tech or post here in request an installer. What you're trying to do is not as simple as adding an extra jack and as you've already found out improper wiring will put the DSL signal on your phones. Bottom line if you're uncomfortable doing this find someone that knows what they are doing. Might cost a few bucks but what's your time worth, you've spent quite a bit of time on it already.
EDIT: Never mind you said conductor not pair. Yes you could feed your modem with the Yellow/Black as long as you don't need the same cable to feed the RJ31X as you will need an in and out pair for it.