This manual may also help. This one is different as you don't have to make your own link from L to the relay contact - it looks as though it has been done for you internally.
http://www.enerfoil.com/me-thermostat/install.htm
Strongly recommend contacting the manufacturer unless you are...
You could also try switching on and off the heating output and use a continuity meter to determine which 2 of the terminals are the relay contact. Typically the heating output is a volt-free contact to which you have to put 240V to one end, then one end of the heater element to the other, and...
I used to fix videos and i tell you cat pee is about the most corrosive substance you can add to electrical equipment. As it dries it leaves a nasty crusty mess in its place.
If it's tripping with no appliances plugged in then surely you should be looking for a L-N or L-E short before whacking it with a megger which tests for insulation?
Some light bulbs can "sing" when connected to a dimmer switch. This is probably caused by ringing of the element because the dimmer circuit chops the mains and introduces high order harmonics.