Pete, the switch assembly has a plug on one end (connected to the receiver) and a socket on the other end (connected to the battery). If you plug your battery pack directly into the receiver it will completely bypass the switch setup and prove if this is the problem or not.

You can connect the battery to any spare set of servo output pins on the receiver, just remember that the negative (black) goes to the bottom pin and the positive (red) goes to the centre pin. Top pin is the control wire for the various servos but not present on the battery connection.

From memory the switch assembly (switch, plug, socket & wires) is identical across all model DF 65’s & the DF95 as well. You may however need to use your old switch control wire or bend the new one to fit as V5 & V6 have the switch installed differently