Toggle Switch: The on/off toggle switch (or equivalent rocker switch, etc) gives you the control to turn the compressor on or off at your discretion. You must use an on/off switch regardless if your system has an air tank or no air tank. When not using the compressor, leave your toggle switch in the off position. The on/off toggle switch controls the function of the relay and if using an air tank, the pressure switch. Failure to use an on/off switch will void your compressor warranty.