I started off controlling my 2/3 fridge 1/3 freezer with just an stc1000 controller popular on ebay, your typical aquarium controller with the default 10A relay – more than adequate for your average 160-250W fridge.
The heating output controlled a 60W tubular greenhouse heater and the cooling output just switched the fridge on and off, the NTC probe being taped to the outside of the FV. I was more than a little nervous drilling the holes for the probe and the tubular heater as I wasn’t sure where the coolant pipes were routed…

I then came across the Brewpi project… It uses two probes, one in the beer and one monitoring the fridge air temperature and  the best place to put the probes inside the thermostat housing. Since it’s an old fridge with no auto defrost function This was duely removed the wires linked  thus making the fridge cool permanently.Both the heater and fridge retained their UK 3 pin mains plugs

 
Thermostat before it was removed

 

 

 

 

 

 

Thermostat removed, light ready for removal , since the light needs a live and Neutral it was easy to work out the live feed and thermostat live switched return. I then just shorted them.

 

 

 

 

 

 

4 wire DIN to 3 wire DIN sockets for probes

Note the pcb mounted probe that I will later use for the fridge ambient air temperature

 

 

 

 

 

 

the 4 to 3 wire DIN  safely in the thermostat housing. Using 2 waterproof probes for testing in this shot. I drilled through the fridge wall where the mechanical switch was housed but in retrospect I should have pulled the 4 core through from the back using the old thermostat wiring as a pull.