This is NOT really the seatbelt interlock relay ( althought lot of ppl knows it like that ), but the seatbelt OVERRIDE OR RESET SWITCH for the interlock system. Jumping out both yellow wires make work the system like this switch is allways activated, overriding the interlock system.
Black wire is ground and is attached to one of the wiper motor mounts. A blue wire comes from ignition switch and is positive, you can link those to if you wish a firework show LOL.
Interlock system can make not being able to crank up the engine, yes, but maybe because is working good and you are not following the seatbelt fastening sequence ( what could be is still in working order ), some of the sensors system is not working or interlock box is not working propperly. Or maybe some part of the system is not plugged.
The interlock box not just controls the crank up order system with the seatbelts fastening requirement, but also controls ALL the warning systems ( lights and buzzers ) of the car, such as seatbelt light and buzzer, key in warning buzzer and lights on warning buzzer.
On previous years all these buzzers were different ones, one for each system, but on 74 is just one buzzer for all the warning signals, with this control box controling it.
The interlock control box, or relay how some ppl calls it is a plastic box down the dash frame, between glove box and ashtray which can be blue if auto car, white off if manual car or orange if built for Canada and some other countries where Federal seatbelt regulations were not mandatory
