What is this harness for?

I think the seatbelt interlock was only for 1974 and, due to the nightmare it was, they scrapped it in 1975. Perhaps a few early build 1975 cars have it though.

However, my 1975 does have that other contraption in the photo but it’s not a seatbelt interlock. It’s been a while since I played around with it so I’d be guessing at what it is now. It’s mounted just in front of the electronic ignition box on the drivers fender.