The SOG System is incredible easy to fault find on as it only has one electrical connection to test.
Are you sure the SOG System is faulty ? Put your ear next to the SOG Fan housing and listen whilst someone opens and closes the toilet flap with the electric supply to the water pump enabled and toilet flush operational, you should hear a quiet drone noise from the fan when the toilet flap is open.
First you need to ascertain if its a mechanical problem with the microswitch coming unseated or damaged, open your toilet cassette door.
If you have a SOG A/B/F/D then the microswitch will be inside the compartment on a small L shaped aluminium bracket stuck next to the slider mechanism. So get someone inside the motorhome/caravan to operate the toilet flat whilst you are looking at the underside of the compartment where the toilet cassette normal is situated and you will see a plastic slot mechanism which moves 90 degrees. The SOG microswitch /plate will be alongside this. Check that when the flap is opened that you can see/hear the click of the microswitch lever being operated.
Next check the supply is available for the SOG Fan, the fan has two wires red+ and black- which are normally tapped into the supply within the toilet compartment which operates the electric flush.
Use a Multimeter set to DC Volts and check you have +12v available across those wire pairs when the flap on the toilet is opened (Remembering that the supply is only available when the water pump switch on your vehicle control panel is enabled usually)
If no supply then the problem is elsewhere within your vehicle or the connections aren't being made correctly to the vehicle supply.
If supply is available and the microswitch is ok then almost certainly the fan itself has failed. These are easily swapped and are available for sale on Outdoorbits if out of the normal warranty period of 2 years.