Chrysler factory info about the 1974 Seat belt Interlock system here:
MyMopar - Mopar Forums & Information - Browse MTSC by Model Year - 1974
The schematic below will give you starting point for troubleshooting the start. When the key is turned to start, only the Ignition 2 and Starter relay wires are connected within the switch.
As you know by now, 73 and 74 are not the same - especially with respect to the buzzer and interlock. So exactly how that, including the overide, ties in will be the puzzle for you to solve.
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