Before you jump to tender tether, how clean are the wheels and pick up rollers? Clean and ensure they are ok. Next you do need to inspect the engine.
This engine has the PS-2 5V board in the engine, so the tether would not effect smoke or lights, only sound rear coupler and battery connection. In DCS this engine would run with out tender attached.
Many times bulbs are loose on these.
Check tether connection at rear of engine. Many times solder joints crack and need to be resoldered. Also make sure wires plugged into PS-2 board fully.
You can check the tether, but again that only effects sounds, rear coupler, and motion in conventional (battery). If it play shutdown sounds when you turn the track power off, the tether is not the cause of your issues. It is something in the engine. G