What is the best way to defeat the interlock on a 1974?

How does the interlock function, i.e. what does it prevent from happening to keep the car from running?

I see on the wiring diagram that both seat-belt switches (and their things) get their power from and are grounded by an electronic "Seat-belt warning system relay and integrated buzzer" (J-34 on the diagram).

I don't know that the car won't start since mine was disconnected (read unplugged) when I got the car. but there are only two states... shorted or not. Somebody will know this, but if it were me:

1. take the passenger seat out
2. unplug the switch
3. Turn the ignition on (no starter of course)

If the buzzer buzzes, then short the two wires and make it go out. Should take you 30 minutes with a 10mm rachet.

Good luck!

Under passenger seat, look at the relay assembly. Two big yellow wires ... disconnect and splice them together ... no more interlock and car will start.

As left photo after I removed the entire component:

Click to view attachment

The whole process was somewhate intuitive after a bit of review of the wiring diagram. The main thing is getting a good splice of the yellow ignition wire.

As been said, connect the yellow wires together. There is a black wire with a red stripe that is hot with the key. Tape the end of it off so it won't ground out......

The easiest way is to use a double male connector, its easily reversible. I am told this is the way dealers did it.

BTW, the seat will come out by sliding it all the way forward. No tools are required.