I have a 90amp Castle Creations Talon ESC. Can anyone help clarify the manual statement "Always disconnect the red power wire on the throttle lead when an external battery is employed in the receiver circuit."

It appears the statement says to cut the red wire on the plug from the ESC that is plugged into the throttle channel of the receiver if I use a NiMh to power the rx and servos.

Thank you

That's what its saying. Though you're best to use the tip of an xacto knife to carefully lift the plastic retaining tab where the pin slides into the connector. Lift the tab, slide the pin out and tape it off. That way if you use the ESC is something else that uses the BEC or sell it, then all you have to do is slide that pin into the connector and it will snap in place good as new.

Thank you Andy!

What would be the harm if the red wire was not disconnected?

Electronics run on smoke inside the wires, what you propose risks letting out that smoke.