'ey Luke, I've reverse-engineered a keyboard before in about half an afternoon. It was a dead one, mind you (my mother had emptied a cup of orange Crystal Lite into it!) but I got a fair idea from it.

The method you're looking for is not following traces, but rather using a multimeter set to continuity (or diode test) and hook-probes (google if unfamiliar). Two sheets of contacts, so two connectors, you know?

So, you hook one hook-probe to the first pin on the bottom-side connector, and the other probe to the first pin on the top-side, and you find what key connects them. Move the top-side hook-probe over one pin and do the same thing. Once you've gotten all the top-side pins, move the bottom-side over one and start the bottom-side over again at pin one.

If you get bored easily (or zone out quickly) -- Pandora and a decent pair of PC speakers really helps ;) Logitech makes okay ones for this that are pretty cheap (audiophiles will beg to differ).