Look at the pilot truck for a broken wire. That was where my problem started, the factory wire was very stiff. I replaced with a length of super-flex, than looking further l saw the tender had the capability of all wheel power pick-up. Just ran some super-flex there and and made up a plug and connected to power feed wires on the engine. I did this first on the PE Berk and than on my NKP Berk, now nothing stops either one.
While you have the shell off the engine and or the tender check to make sure all the plugs are secure