What is this thing???

No picture but I'll bet that I know anyway...
Red button on it, right?
That is a 1974 ONE year only device. Here is a summary.....
For the 1974 model year, the Federal government mandated that American cars had to be equipped with devices that required the SEAT BELTS BE BUCKLED before the car could be started. Many components were integrated to make this happen. Sensors are in the seats to detect weight. There is a blue electrical box under the dash near the steering column that has several wires going into it. THIS was the brain/command center of the system. That small box under the hood was a RESET for the system. If a person tried THREE times to start the car without the seat belts buckled, the car shut down. That red button reset the system. You should seek out a 1973 Factory Service Manual and compare the wiring diagram to yours. THEN remove any wire associated with that seat belt system.
OR just unplug it and see what happens!