I have the Bachmann Spectrum 55 ton SHAY  item #82698.  While lubricating the engine.  I noticed as the Tank car was being handled the truck had a lot of movement.  Mine doesn't have that much movement and will derail on 30 degree switches.

  Then it shows two plugs to connect to the engine.  I have the two wires but on a single connection bar, and the wires restrict the movement of the extra tank causing it to derail on 30 degree curves.

  And I only have the single hole connection to the locomotive, not a problem just wondering why the difference?