Does anyone know more details about how the O2 sensor heater wires coming from the MAS relay work? Specifically, is it strictly key on, apply power to these wires? Or does the ECU cut power to the heater wires if the sensor is warmed up enough?

I'm trying to determine if this source of power is good enough for a wideband O2 controller. I don't really feel like hooking into another area for power, but I will go cigarette lighter if the original O2 heater from the MAS relay is not a reliable 12V switched power source.