Why is my transistor always transmitting? I want to use a transistor to turn on and of an electric magnet, I have hooked up a transistor like this: 







simulate this circuit &ndash; Schematic created using CircuitLab

The blue wire goes to the magnet and the white wire goes to the ground:



Regardless of if the arduino is on or off(I can even unplug port 12 from the arduino, the magnet is still on, the circuit never closes. What do I need to do to make the transistor turn off?
Darlington transistors are very sensitive; even putting your hand near it can be enough to turn it on. Either tie the base to ground with a large resistor or switch to a MOSFET with its gate tied to ground through same. In either case put a diode backwards across the coil to absorb the energy from the coil when it de-energizes so that the transistor is not damaged.