Seat Belt Interlock Relay, Late 74-76’ - how does it work? Options

[Superhawk996]

For those of you that despise the seatbelt / starter interlock and the horrific screeching noise the seat belt buzzer makes - let me say I understand completely. As I’ve been playing with this on the bench my wife now hates the noise just as much as I do.

This thread is going to explain how it works and how to bench test it over the coming days.




Credit is owed to @JeffBowlsby , @Bdstone914 , and @Montreal914 for providing me with donor parts that will make this thread possible.

Eventually I will post the schematic of this ridiculous conglomeration of components. I hope to eventually put the circuit in LTSpice to help verify its theoretical operation. I make no warranty as to the accuracy of the schematic - this is just me satisfying my own curiosity.



If you have no interest in my personality defects that would lead me to take on this little project; ignore this thread.

If you have a late car with an in-op system and eventually want to get it working - this thread is for you.

Toward the end I’ll share some ideas on how to get rid of or to change that horrific buzzer noise.

[Superhawk996]

So at this point we are though the sit down & buckle up portion of the “logic” sequence needed to start.

The next thing to do is to apply 12v power to pin C (circled in orange) - in the subsequent photo this will be a yellow wire with +12v on it coming into pin C.



This is the same as turning the key to the start position

The result is a click as the starter interlock relay energizes


To show that the starter interlock solenoid has closed and connected pin C to pin 50 I’ve rigged up a lamp with the yellow wire on pin 50 and the other side of the lamp to ground. This current path is what the yellow starter solenoid wire will flow through in vehicle.




I’ll attach a video here a little later to show this sequence of events and so you can hear the starter solenoid interlock relay pull in.

https://www.youtube.com/watch?v=KFhefyS-sgc?si=7lUXcryHdgSQZV7Z


Note: @sirandy - something squirrelly going on where pictures between post 36 & 37 are somehow inter related - editing in one post screws up photos in the other ?? Never seen this before. Sort of seems the photos for post 36 are resident in post 37.