What Kern said above.
What they did was split the yellow starter wire at the box and the box either allows or disallows the starter to be engaged depending on the inputs from the other wires. I don't remember what all the other wires are, but I think there were power on, door ajar, certainly seatbelt sensors, etc. If the right inputs were received, the box connected the yellow wires in the plug, allowing for the starter to be engaged.
There are a couple of ways to defeat this without removing anything.
There are 2 yellow wires going into the bulkhead connector on the interior side of the plug, swap those 2 and the ignition will work without having to worry about the box. I did this on my '74 and completely removed the box entirely. I like this option best as it basically wires the car to work as if there is never was a seatbelt interlock.
I think you can unplug the seat belt sensors as well. My Duster worked for years with the box plugged in and my guess is that it was only because the seatbelts were never connected. But it could also be that there are sensors under the seat so the box knows if someone were sitting in the seat, and my car never had those either. So maybe you need both unplugged? Or maybe one or the other is enough.
You could also cut and splice together the 2 yellow wires at the box.
Last option is the built in one. There should be a small box on the rear of the drivers side fender apron with a red button. Pop the hood, turn the key to run and then the key will work to start the car. But you will have to do this every time if you have a problem with the box.
This all assumes you have a '74 model year car. Seems like the '75-76 cars had a box as well, but it wasn't a seatbelt interlock?
