[ame="http://www.youtube.com/watch?v=gg0geLWGpWg"]MTSC - 1972, Volume 72-5 1972 Seat Belt Warning System - YouTube[/ame]
I would say that referring to about page 12 and after in the pdf, pulling the relay and buzzer would be what you want. It's "up under the dash" somewhere to the right of the column or starting approx at the 16 minute mark in the movie