this connector is on the passenger side firewall of my 74 the square black plastic box above it is the cap that fits over top of it. nothing plugs into it. I cant seem to find it on my wiring diagram.

 

Andy,

It is the seat belt override switch. A one year only device (fortunately!) that most people bypassed. If your car starts and runs, then it more than likely has been bypassed and you need not worry about it. That cap looks non-genuine, the factory caps have a hole in the middle into which you can push a pencil etc. to reset the switch when your car won't start.

I'm guessing here, but I think it was installed so that if you or a passenger did not want to wear a seat belt, the sensors in the seat told the switch that the seat belt had not been fastened and the starter would be disabled. Pushing in the switch on the factory black cap allowed the engine to be started while a seat belt was not buckled (with a person or bag of shopping, etc. sitting on it).

Hope this helps.

Regards from Down Under.

aussiejohn

 

John is correct. It is the seatbelt interlock switch. Buckle up your doggie on the passenger seat or the car will not start. It was mandated for the model year 1974 but the law repealed for 1975 owing to public outcry. Most if not all interlock systems are now disabled in 1974 cars still on the road. If your car starts don't worry about it.

 

The Seat Belt Interlock was the Government's first attempt at "passive" restraint systems. Effective August 1973, Federal law required that all cars sold in the US, had to have either a passive restraint system (air bags or automatic seat belts) or a seat belt interlock.

If a car's front seat passengers didn't have their seat belts buckled, the interlock wouldn't allow the car to start. Unfortunately, even with the belts buckled, the car didn't always start. The override allowed one start of the car, without buckling the belts. It was installed in the engine compartment, to discourage people from trying to use it every time they drove the car. People quickly learned how to disable the system.

Within months of it's introduction, Congress was inundated with complaints about the systems. The law was repealed on October 31, 1974. 1975 models, built prior to October 74, also had the seat belt interlock.

 

You can see the seat weight sensor in this pic. I "believe" (my memory is failing me) it kicked in at about 20lbs.

 

thanks for all the great info guys thats why i read this forum everyday. I would like to keep my car stock as possible but i dont think i will touch the switch car starts great maybe i paint it up nice