Erik,

You're likely to run into problems starting off that way; try to follow it through and you'll see what I mean.

The trick is to be able to positively identify one conductor at both ends to provide a reference point. With only one round trip allowed, you must be able to identify that first conductor from down in the basement. If you start with six wires all linked into three pairs, you won't be able to do that.

I love these sort of brain teasers, as they're a great exercise in logical thinking AND have a practical application.

Keep working on it! [Linked Image]