not wanting to cast unhelpful doubt on the existance of the shore supply connector for the 379's, but my understanding is they don't have them. On DC/DV units the shore supply connector is linked to the main DC bus line via the shoegear earthing/isolation switch, with interlock keys being needed to be relocated to facilitate this. My understanding of the 379's is due to the ability of simply being able to get an overhead supply in a depot, there is no need for a shore supply socket.
I am also lead to believe that there is not an alternative 'traction disable' switch on AC only units (this switch is in the shore supply changeover switch, and prevents traction power from being taken when not required in depot)