75 Duster electrical boxes

Yeah from 73 up they added more emissions crap year after year. That thingy in the speedo cable was emissions or economy related also. I forget did it turn on a lamp in the dash at a certain speed or what exactly. Maybe someone can link a earlier thread of its discussion.
I think the seatbelt interlock that would disable start was one year only, 1974 model. 75 and later was limited to seatbelt warning lamp. Good luck with it.