It's something to do with the seatbelt interlock, 1974 only. Do a search for "Yellow Box" you'll find some answers, they can also be gray like yours. If Jamie was around he'd tell you about it.
wow who knew thanks guys for the help who wants to buy it? trade for a grabber hood? or complete mav ??? sounds fair to me
Looks similar (but not identical) to the seat belt interlock on my 75, like was posted by others... However I thought they were all yellow.