Is there any way I can turn off the 5V pin? I'm trying to find a way I can toggle the 5V pin to turn on/off. I want the voltage to pass to another wire at a certain point. It should be off and then when something happens, the 5V should turn on. 

How can I do this?
For energy-efficient switching (along with relatively high-current capability), I recommend using a Darlington transistor connected to one of the output pins (digital for on/off, analogue for variable). Then you would just call  pinMode(A0, OUTPUT); followed by digitalWrite(A0, HIGH); Here is a sketch I made demonstrating what I mean:


Note that a normal transistor would draw more current from the Arduino's pin, which could be bad for the Arduino, and which would waste energy.