An assembly includes at least one electronic component, a bus bar electrically connected to the electronic component and having a connection portion, a case receiving both the electronic component and the bus bar and having first and second openings, and a drop prevention member having a drop prevention wall. The connection portion of the bus bar is to be connected with a terminal of an external connector by engaging a first engaging member to be placed inside the case through the first opening and a second engaging member provided in the external connector. In the assembly, there is defined, by the drop prevention wall, the connection portion of the bus bar, and part of the external connector, a confinement space for confining the first engaging member and thereby preventing it from dropping outside the confinement space during establishment of the engagement between the first and second engaging members.