Thanks for the replies. The ess dual does supply the Y harness. I am aware of the esc box. Unfortunately, for this esc which was developed jointly by flysky n hobby wing, the ch 2 is interfaced into the esc and motor as a 3 in1. It only has ch 1 for servo, channel 3 n 4 are for its light features. This was told to me by the tech support at flysky customer service.
New question: is it possible to tap into the wires leading to the rc 390 motors and link the ess from there? Since the ess dual needs the throttle revs to calibrate won't the motors produce revs too? Or will the voltage be different? But the motors have only 2 wires and the connectors to esc has 3. Is it viable? Thanks again.