6v6gt:
Not really!Use your original diagram. Short out SW2. Add a switch between D10 and R3.
I see, that could work for me. But I also wanted to hook up an LED, so it shows when the heater is heating up, but turns off when the switch is turned off (the point of the switch is to turn the heater off but still keep the LCD and all the rest on). Would this work?
I know the parallel circuit divides the current, would that be a problem?
Thank you guys again for the great help.
EDIT: Never mind that. Instead, I'll connect the switch to 5V and an input pin, digitalRead that pin and use that value to turn on both heater and LED. That should do it.