How can I find out which ethernet cable goes where?
I had a similar situation with a big bundle of plain CAT-5 cables in the basement. Each cable went to one random room in the house.

To determine which cable was associated with a room, I did the following simple experiment:


In the room, twist together two of the conductors to each other. I connected orange to dotted orange, just because it was easy to remember. Doesn't matter which two you twist together.
In the basement, for each CAT-5 cable, use an Ohmmeter to measure the resistance across orange and dotted orange. For every cable except the one where you connected the conductors, you'll see infinite resistance. For the one where you connected the conductors, you'll see no resistance.
Don't forget to untwist the leads you connected.


An ohmmeter is built into any cheap multimeter like this $30 model from Radio Shack and since I had one around anyway for other electrical projects this was easier than buying specialized network testing equipment.