I'm not going to go over how to build the Ember kit, LEK has a great tutorial for it, (they also have a tutorial on doing exactly this but for a coffee pot). I'm going to take you though how to hack it into a crock pot. Really all we're doing here is mounting the controller, connecting 3 wires, and placing the thermometer. So even if you have a different crock pot, or something totally different, most everything here will still be of some use to you. I'm not going to go into why anything works in this; I'm aiming at a audience that has minimal electronics experience since there were a lot of people at the class that wanted a sous vide machine but had never soldered or done any electronics work before.
Step 1: Break It Open
Once its open take a look at the wires; they're should be 3 that carry power and depending on the design another set connected to the thermometer. Of the power wires, one will connect from where ever the power cable comes in to the heating element, one will go from the power cable entrance to the existing controller, and the last one will go from the controller to the other end of the heating element. You can take out the thermometer and save it from another project because the ember kit already has one its calibrated to.
Remove any mounting screws and cut all of the cables attached to the existing controller. Don't cut the wire from the power cord to the heating element, only the ones on the controller. If your wires aren't colored differently you can label them.
Step 2: Mount the Ember
Drill holes in the Ember case for the screws first so you don't crask the plastic. Once I attached the box to the face plate I drilled a large hole though both pieces of plastic, this is where the thermometer and wires will go though.
Hold the Ember up to where you will mount it and figure out how long you need the wires to be to reach the ones in the crockpot. Trim off excess length and strip the ends of the wires. Also figure out where the thermometer is going to go, you might need to extend it with some of the wire you just trimmed to get it in a good place. (Try to put it in the middle, not to close to the heating element.)
Thread the wires though the hole you drilled in the Ember case and into the crockpot, now mount the ember.
Step 3: Connect It All
You can attach the black and white wires from the ember to power and plug it in to make sure it works still
In my crockpot I was very disappointed that all the colors didn't match up. Red and white are switched from the old controller to the Ember.
Step 4: Sugru the Thermometer
Step 5: Wrap It Up!
Let the Sugru set over night and then make some food!