Signal Wiring & Power Wiring
Signal wiring deals with input signals (generated by the temperature sensor) and output signals (generated by the temperature controller).
Power wiring deals with supply power to the temperature and power controllers and the current that is ultimately delivered to the heating element.
Signal wiring is less straight forward than power wiring. Not only does it have to conform to circuit design but also installed in such a way as to minimize the negative effects of electrical noise present in any thermal system.