Ford Mid-Size Cars 1971-1985 Repair Guide

1974-75 Models


All 1974 and some 1975 Ford and Mercury vehicles are equipped with the Federally required starter interlock system. The purpose of this system is to encourage the use of seat belts.

The system includes a warning light and buzzer (as in late 1972 and 1973), weight sensors in the front seats, switches in the out-board front seat belt retractors, and an electronic control module. The center front seat is tied into the warning light and buzzer system, but not into the starter interlock.

The electronic control module requires that the driver and right front passenger first sit down, then pull out their seat belts. If this is not done, the starter will not operate, but the light and buzzer will. The sequence must be followed each time the engine is started unless the driver and passenger have remained seated and buckled. If the seat belts have been pulled out and left buckled, the engine will not start. The switches in the retractors must be cycled for each start. If the belts are released after the start, the light and buzzer will operate.

If the system should fail, preventing starting, the interlock by-pass switch under the hood can be used. This switch permits one start without interference from the interlock system. This by-pass switch can also be used for servicing purposes.


See Figure 1

If the starter will not crank or the warning buzzer will not shut off, perform the following checks:


Front seat occupant sits on a pre-buckled seat belt.


Unbuckle the pre-buckled belt, fully retract, extract, and then rebuckle the belt.


The front seat occupants are buckled, but the starter will not crank.


The unoccupied seat sensor switch stuck closed before the seat was occupied. Reset the unoccupied seat sensor switches by applying and then releasing 50 lbs. (22 kg) or more of weight to the seat directly over the seat sensor switches.


Starter will not crank with a heavy parcel on the front seat.


Buckle the seat belt around the parcel or move it somewhere else in the car. Unbuckle the seat belt when the parcel is removed from the front seat.


Starter will not crank due to starter interlock system component failure.


An emergency starter interlock override switch is located under the hood on the fender apron. Depress the red push button on the switch and release it. This will allow one complete cycle of the ignition key from OFF to START and back it OFF . Do not tape the button down as this will result in the deactivation of the override feature.

Click image to see an enlarged view

Fig. Fig. 1: Seat belt/starter interlock system circuit-1974-75