Addition of limit switch for power supply stops circuit from working. Circuit works fine without the switch?
Your limit switch is normally open, and closes when the limit is reached. 

I expect you want to have your circuit powered when the servo is in the middle of the range, and un-powered when it reaches the limit, your switch does the exact opposite powering the circuit only when you're at the limit.

To do this you need a normally closed limit switch (or a limit switch which has both sorts of contacts).