do you not have an on-off switch on your esc? If not I'm guessing it turns on when you plug in your battery. IMO I would leave it, if you really want to put in a switch I would believe there are much better places to put it.
A loose connection on that set up would probably be where the wire attaches to the bullet connectors or where the wires are soldered to the motor. You will need to figure out where the loose connection is then repair it by soldering it.