GM Cadillac 1967-1989 Repair Guide

Seat Belt/Starter Interlock (1974-75)


As required by law, all 1974 and some 1975 Cadillac 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, the engine cannot be started.

If, after the car is started, the seat belts are unfastened, a warning buzzer and light will be activated in a similar manner to that described above for 1972-73 models.

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 or sudden stop.

The lap belts use the same rachet-type retractors that the 1972-73 models use. 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 1972-73.

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 over-ride switch is located under the hood. This is a one start switch and it must be reset each time it is used.


Since the requirement for the interlock system was dropped during the 1975 model year, those systems installed on cars built earlier may now be legally disabled. The seat belt warning light is still required.

  1. Disconnect the negative battery cable.
  3. Locate the interlock harness connector under the left side of the instrument panel on or near the fuse block. It has orange, yellow, and green leads.
  5. Cut and tape the ends of the green wire on the body side of the connector.
  7. Remove the buzzer from the fuse block or connector.