I have a trex 600 with a castle ice 100 , I am running a battery for the controls and battery for the motor, Do I have to turn off the BEC from the ESC or can I run it along with the receiver battery for redundancy I an running a 3GX controller if that matters

I always run either/or but not both

Castle BECs are not equipped to tack back-current from a battery.
If you want to run both, you can use a battery buffer such as
http://www.western-robotics.com/BBFR
otherwise disconnect the BEC from the circuit by cutting or removing the red wire (or using an extention cable the the red wire cut).

Duplicate.

No need to cut the red wire on the ESC. All you need to do is remove the red connector pin from the connector housing. The wires are crimped into the terminal and then inserted into the connector housing far enough to engage the retainer. By pushing in on the red wire you will be able to use an Exacto knife or straight pin to lift the retainer so that the red wire terminal can be slid out of the connector housing. Either wrap the terminal with electrical tape or use a piece of heat shrink. Doing it this way enables you to return the ESC to original condition if you wanted.
Found this video that shows the process but I found it works better if you first push the wire into the housing in order to clear the small plastic tab that locks the terminal into the housing.

How to disconnect a wire from from a servo plug (1 min 53 sec)

Originally Posted by Philkoury

No need to cut the red wire on the ESC. All you need to do is remove the red connector pin from the connector housing.

Exactly what I do incase you sell it or decide to use the BEC.