If you're asking about a 74, Federal Motor Vehicle Safety Standards required the 74s to be equipped with a seat belt starter interlock and reminder system (annoying buzzer). The driver and outer most passenger had to fasten their seat belt in order to start the car. The two outer most seat belts had weight sensitive switches under the seat, and would not crank if not buckled. (A grocery bag had to be seatbelted if heavy enough.)
My 74 Dart Sport had a bench seat, and I used to use the center passenger belt to buckle into the driver's connector. I was then able to start the car without actually wearing my belt. Eventually those of us inconvenienced by having to buckle the belts just unplugged the switch under the seat. No more buzzer, no more necessity to fasten belt to start engine.
The device you show in the pictures (larger pictures would have been better) was a manual by-pass switch located under the hood, on the driver's side of the dash panel, between the ballast resistor and windshield washer bottle. In the unlikely event the engine would not start, even though all front seat occupants were properly wearing belts, this emergency by-pass switch could be used. Procedures were:
1. Ignition Switch must be in the "ON" position to activate the by-pass switch.
2. Depress the center plunger of the by-pass switch with an object such as a pencil. (The pointed end.)
3. Turn ignition switch to "Start" position and start engine. The engine can be started and restarted until the ignition switch has been turned "OFF".
4. Should you turn the ignition switch to the "OFF" position, the by-pass switch will release and instructions 1-2-3 must be repeated.
Occasionaly your car might not want to crank. Take a pencil out of the glovebox and follow the above instuctions. I don't believe this by-pass switch was on cars after 74 nor was the seatbelt buckled a must to start the car after 74. However they did have buzzers after 74. Those could also be disconnected under the dash without affecting starting.
By the way Steptoe, I grew up in Pascagoula where I bought my 74 thirty-four years ago. Still have it. PM me if you have any more questions. Did you do Cruising the Coast two weekends ago? Highway 90 is still a mess three years after Katrina.
