Item description for Mactronix Part (??) Rear Shelf (??) 17449-001 Rev. 1 Not sure what it is

I don't know what this is but I think that it might be a Mactronix part because it came with another part that was marked "Mactronix". One one end of the cable it says "J26 For Left Rear Shelf" and on the other end of the cable it has "174510-002 REV-2 SEC003". On a plate that is attached to the main unit it has "17449-00 REV. 1 CAD 9-3-98". The overall dimensions are about 22-1/2" long, 7-1/4" deep and 7-1/2" tall. Everything that is included is shown in the pictures.