You need a "Y" harness, not the extra wire coming off the power switch, it is for charging.
Disconnect one of your servos and connect the power switch into that port on the Rx.
Now connect the DSC where the power switch was, and turn everything on.
This is only for a test, as you won't be able to test both servos.
FYI: If you a 3 ch Rx, just connect the power switch to CH 3. Then put the DSC in the DSC/Batt port.