First things first. I'm not an electrician. If you're uncomfortable around electricity, find somebody who is. Always unplug the fridge from the wall before working on any of the wiring. Seriously. Also, label all the wires as you're doing cuts. It's easy to forget which is which. Finally pick up wiring that matches what's installed in your fridge - it should say somewhere along the length of wiring. Mine was 18AWG stranded.
Remove the whole control panel. There are a couple of screws. hold on to them. You should see something like this inside
These are the thermostats you're replacing
Side note - I left the actual thermostat/dials in even though they aren't hooked up to anything any more.
The green/yellow wire on the side is ground. There's nothing in the new system that you'll be hooking up to ground, so just remove it and tape it off or something. Your hot will probably be black. The other colors go to the defrost board. In my fridge orange was the freezer controller, and the purple/white was for the fridge. DON"T take the colors as gospel. yours could (probably will) be different. There was a diagram on the box containing the circuit board. Made it easy. You also need to know which wire is a plain neutral. If I remember correctly it was one of the wires coming off the light bulb.
The wiring diagram isn't too hard, but it will take a bit of thought and planning. One you understand what needs to happen everything falls into place. This is the idea:
You want to take the hot lead and split it off to the main power supply for both controllers, to one terminal on the freezer size, and two terminals on the fridge side. Five total, if my math is correct. Doing this gives you power to each terminal so the next part makes sense. Remember - you are simply replacing the control dials (thermostats) and running the wires over to the new digital controllers. Simpler, once you think of it that way. I also think of the colored wires as specific neutral wires so I didn't get confused.
To control the freezer, run a wire between the orange (mine) freezer control coming out of the circuit board (was previously attached to the freezer thermostat), and send it over to the empty terminal on the freezer/cool controller.
Fridge cool control: Same idea - control board to the empty fridge/cool terminal.
Fridge/heat: A little bit trickier, but you need two lengths of wire that will give you enough slack to put your heating device (probably) in the bottom of the fridge. One of those wires will connect the controller (heat) to the heat source (I used a CERAMIC bulb base from HD with a ceramic reptile heater- 100W). The other wire goes from the other terminal on your heat source to the neutral wire back in your wire bundle. You remembered which one was neutral, right?
You need to run all these wires through a hole somehow. Make a hole.
And run all the wires through (this is a good time to make a hole in the center wall for you freezer probe)… run your probe wires, too. It might be helpful to organize all these same-colored wires with small zip ties. It keep everything neat and tidy.
Since you labeled all your wires it should be easy to connect them to the proper spot on the controllers. Put the retainer clips in place, and pack the empty spaces with styrofoam or some other kind of insulation.
See what I did there? "FG Control" is the wire that leads back to the fridge control wire.
It might be helpful to check to make sure everything is working before buttoning up all the way. I tested with a light bulb.
Here's my black IPA with the ceramic heater. I bought a 120VAC mushroom fan to keep the circulation going when the heat is on. If you do that, wire it in parallel with the heat lamp (make a Y-split off the two wires coming from the bundle and attach).
Making kit look nice
I wrapped the wires in some spiral-cut sheathing I picked up from… I don't remember. Home Depot has it. Fry's has it. It's common stuff. Cheap.
Done. Make some beer
Here are some suggested starting points on the settings. You may find you want something different.
F1: Cold. What's your preference
F3: 10 (minutes)
F4: don't touch
F1: Depends on your yeast
F3: 10 (minutes)
F4: don't touch