Create an Actor variable inside the Electric Panel blueprint, and expose it (a little eye icon next to the variable name). Thus this variable will be available to you in the viewport, and you’ll be able to select the Door or any other actor with eye-dropper or by typing in its name. And then you can work with this variable in the Panel BP.
And you’d want to use Interfaces here, since you might want to control various objects, not just Doors. With Interfaces, you won’t have to Cast to a number of blueprints.