I have had a couple questions regarding this, so I figured I would make a quick post with a picture.
shows the inside of the Ranco controller. In the picture the power comes in from the front of the two wires and the fridge plugs into the back (not that it matters). If you take an extension cord and cut it at an appropriate place you can then wire it such that:
The black wire from the part that plugs into the wall gets a wire nut or solder to split it into two. One of those goes into the switch portion of the relay (the back terminal block) the other one goes into the controller power (front terminal block).
The black wire from the part where the freezer will plug into goes into the switch portion of the relay next to the other black wire.
The white wires from both sides need to be tied together with an additional piece of wire which will go to the controller power portion of the terminal block. (common)
The green wires need to be tied together.
for a larger view.
Hope this helps.