When I ran my Tekin RS in 1/12th, I used to solder a servo connector directly to the battery posts and run the booster directly from that to the receiver. Double side tape the ESC power switch facing the chassis to keep it off permanently and prevent "helpful" corner marshals from turning it on and overheating the BEC. No need to remove the red RX wire. I don't own an RSX, but this was correct for the RS.