Ok, long enough time for the joke.
You see the three wires going into the thermostat, right?
The black one is "hot" or "Live". The hot wire is almost always the color of insulation that looks most burnt.
That means that the other two wires are probably an earth - say the green one (you'll notice that it's bolted to the frame) - and the yellow one would then be the power lead to the compressor.
This diagram from a UK homebrew forum may help:
The STC-1000 has no interest in the "Earth" lead because it's housing is plastic.
The white lead is the "Neutral" - you will need to tie into that to power the STC-1000.
Oh, and ALWAYS switch the hot lead. Never the neutral or earth.
(Note that i use the term "Earth" here because it is more clear than "Ground". A lot of electrics have "ground" voltages that are relative. "Earth" here means literally the earth. Dirt. Quite literally an 8 foot long copper-clad steel spike driven into the earth next to your house. At least, that's what the earth prong of your outlets SHOULD be tied to. It might be tied to the neutral from the pole.)