T12 has heater and thermocouple in serial.
That trace that you need to cut is to split power (+24V) and input of U3 amplifier (this is to know what is the temperature on the thermocouple).
I hope I explained it clearly. If not, just ask.
So you need to connect TC+ to JBC (also where is says: "this trace wrong on some boards"). So your thermocouple will go to R12D (pin 5).
Everything understandable?
EDIT: I guess I was a little bit too slow