Maybe I'm wrong, but if you set it up that way, wouldn't you have a battery voltage input on one side of the Y, and a receiver signal out on the other side of the Y, all trying to run into the same channel?
ORIGINAL: wyldman
Put a Y harness in the gear channel 5 and plug the kill servo or switch into one side of the Y harness and the battery into the other side of Y harness. Program and use Channel 5 for the kill switch
Wyldman