Seat belt buzzer and relay question

[Marcin]

Hi

I am trying to make some order with my Monza wiring. I can see 1 black or dark brown wire on the floor. Probably it should be connected to driver seat belt. My Monza is 1976 year so probably with only light and buzzer for driver seat belt. Testing seat belt connection itself I can find that it is open closed all the time and open when seat belt is in use. So I guess that when I connect this black wire to ground warning light and buzzer should be on. But nothing happens. I have tested buzzer and it works so I am missing something. Maybe there is any relay I should check? Or moving AT into D and ignition "on" without engine start is not enough? Any advice?