See Figure 1
In addition to the light and buzzer, a starter interlock was incorporated into the seat belt warning system on some 1974-85 models.
The car cannot be started unless the seat belts are fastened in a specific order. The driver (and front seat passenger) must get into the car, close the door(s), sit down, and then fasten the seat belts. If the seat belts are not fastened, or if they are fastened before the driver (and passenger) sit down, the car will not start, and the light and buzzer will operate. This prevents the belts from being permanently fastened and shoved behind the seats.
In case of a system failure and to make it easier for mechanics working on a car, a manual bypass button is located under the hood. Pushing this button allows 1 free start, i.e., without fastening the seat belt. Each additional free start requires that the button be pushed again.
If a package, handbag, etc., is placed on the passenger's seat, the car may not start, and the light and buzzer may come ON as well, even if there is no one sitting in the seat. Either fasten the seat belt or remove the item.
The following components are used for the seat belt/starter interlock system: a logic module (transistorized), 2 pressure sensitive front seat switches, a starter relay, a bypass (emergency start button, 2 seat belt buckle switches, a warning buzzer, and a warning light.
Repair of the seat belt interlock components is limited to their replacement. Testing the system requires the use of a special tester, which connects to the seat belt/starter interlock system at several points. About the only place that you are likely to find the tester is at your local Subaru dealer. Because of this, repair and testing are best left to a dealer.
If the warning light bulb burns out, access to it may be gained by removing the instrument cluster.