I just used a couple of extra lugs on the terminal strip. I soldered the thermistor between the lugs, soldered the neutral lead of the power cord to one of these lugs, and soldered one of the power transformer primary (black) leads to the other lug. That places the thermistor in series with the AC input. BTW: you can install the thermistor in either the neutral or hot AC lead. I chose the neutral for convenience sake.