Abstract: A pair of electric connection boxes are mounted respectively on a large-size instrument panel and a body panel in an automobile and have respective collective-connecting connector portions. One or both of the electric connection boxes is movably supported through resilient support members (for example 27) such as rubber pieces or springs within an outer frame which is fixedly mounted on the associated panel so as to be self-aligning when the boxes are joined. A bolt (for example 58) is used to fix the connector portions (for example 33, 45) together and also to secure the instrument panel (for example 10) to the body panel (for example 14). In another embodiment, (FIGS. 5-7) an insulating plate (for example 123) having bus bars (for example 122) is resiliently supported within a casing formed by housing parts (for example 120, 121) which are fixed to an instrument panel (for example 110).