As required by law, all 1974 and most 1975 Datsun passenger cars cannot be started until the front seat occupants are seated and have fastened their seat belts. If the proper sequence is not followed, e.g., the occupants fasten the seat belts and then sit on them, the engine cannot be started.
The shoulder harness and lap belt are permanently fastened together, so that they both must be worn. The shoulder harness uses an inertia lock reel to allow freedom of movement under normal driving conditions.
This type of reel locks up when the car decelerates rapidly, as during a crash.
The switches for the interlock system have been removed from the lap belt retractors and placed in the belt buckles. The seat sensors remain the same as those used in 1973.
For ease of service, the car may be started from outside, by reaching in and turning the key, but without depressing the seat sensors.
In case of system failure, an override switch is located under the hood. This is a one-start switch and it must be reset each time it is used.