Seat belt interlock voodo black magic box from the deepest pit of hades. Do a search much has been said about this...
Just for the heck of it, I tried getting rid of that evil box once... then my car wouldn't start. I'm not entirely sure what it does but I had to plug it back in to start my car.
That was a one year only device (1974) it works with the red button located on the drivers side of the engine compartment. It can be bypassed, instructions are on the link below. Seatbelt interlocking system http://1bad6t.com/Maverick/repair/seatbelt_74.html
Interesting.ive got a 75 and its already been bypassed in the engine compartment near as i can tell. So that means i can disconnect under the dash?????
Pretty likely ... most folks had disconnected them back in the day. If you set a bag of groceries on the passenger seat that weighed enough, that box would think there was a person sitting there. Either you buckled that belt, or the car wouldn't start. If anyone needs one, I do have one here out of a 60K mile car. You can have it for the cost of shipping.