Diagnosis and Repair Issues Concerning Your Imperial's Seat Belt Relay


Imperial Home Page -> Repair -> Electrical System -> Power Seats -> Relay

 Question from Roger (1974):

Can any one tell me where the relay is located that keeps a 1974 Imperial from starting if seat belt is not latched if there is weight in seat like a bag of groceries or a person?


From Mike:

This is a somewhat obscure bit of automobilia, used only in the 1974 model year. Those of us afflicted with a car of this vintage (My Other Mopar is a '74) have oft butted heads with this beast. Basically, there is a weight sensor underneath the seats that triggers the seat belts switch to deactivate the ignition unless the belts are buckled. From what I know of this system, it includes the switches in the seatbelts, the weight sensors under the seats, and a relay mounted on the firewall.  

The firewall mounted relay should have a red button on it; if the car is dead (ie starter doesn't make any noise) you may have to press the red button down; this will reset whatever it is that's inside; I think its some sort of circuit breaker. 

 The easy (perhaps intentionally?) way to defeat the system is to simply unplug the sensors on the seat/belt. Without any input, the default condition is to let the car start. 

From Chris:

The idea behind the red button on the firewall was convenience for the mechanic working on the car, using the button, the car can be started without getting in and buckling up. Say for instance the mechanic was going to check the vehicle's timing, he would get his timing light all hooked up, push the red button on the firewall, reach through the window (or open door) and start the car. The red button is a one start per button push deal, preventing it's use to circumvent the seatbelt interlock system.

From Jim:

I don't know about the relays & so forth but I had a 74 Plymouth Fury with the same system. "Motor" (like a Chilton's but better) repair manuals that came out a year or so later had a description and photo of how to defeat the system. It seems that there is some kind of a bow under the dash on the drive's side. It has a printed circuit board and their method was to solder two specific terminals on the board together. The photo clearly identified which two terminals. Its been over 25 years since I did that to the car so I don't remember more details - sorry. Motor manuals are available pretty much anywhere Chilton's manuals are sold. In case they edit things out from time to time, I would personally try going to a public library to see if they have one printed along about 1976 or so. I believe that the book said that the system was the same in all the big Chryslers and that would include the Imperial. When I originally got the car, it was a retired Highway Patrol car and the officer had taken a simpler approach to dealing with it: pull the seatbelt out as if you are going to buckle it, fold the metal end back against the belt and let the seatbelt retract. With the metal end folded backwards, it retracts fully into its rest but the belt is actually pulled out a few inches because the metal end is backwards. The gizmos inside think its buckled and there's no problem.

From Paul:

The reason the safety mechanism is only on '74 is -- The lawmakers mandated it (for '74) and then when they got their new cars they hated it so they repealed it for '75.

This page last updated March 12, 2003.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club