They already have internal loads (resistors) to help balancing the outputs. I've never seen any shutting down without load.
Just send the green wire to gnd (black) to turn it on.
In any case, they have voltage supervisors that will turn It off if any voltage goes out of control.
For very low power, 1A or so, you can use the standby 5V (purple), it's always enabled, no need to turn on the power stage.