That "little green square" is a capacitor. You need to note where all the wires are [u]before[/u] you take anything apart, and then install the new component exactly the way the old one was.

I'm guessing you didn't do that, huh? :o

If you soldered all of the wires to the back of the pot, you have grounded the pickup output, which is why there is no signal coming out.