I have this circuit built (updated to remove short-circuit):
I'm experiencing some weird behavior though that I don't understand.
1. When I close the switch, nothing happens. No current flows through the MOSFET, according to the Ammeter.
2. If I disconnect the ground of the Arduino from the negative terminal of the power supply, current flows through the MOSFET, even when the switch isn't closed!
Have I hooked this up incorrectly? Why is the MOSFET letting current through? Any ideas?
Note: Data Sheet for MOSFET
Note 2: When I use this exact setup but replace the 12V power supply with a battery, and the component with a resistor and an LED, it works fine.