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]

Oh - here’s which relays are which

The starter interlock relay is on the left in green

The buzzer “relay” is on the right in red



The buzzer is actually just a simple relay wired such that when the solenoid coil is energized and pulls in - it disconnects the coil via the relay contacts. The coil de-energizes and the relay returns, the solenoid coil is again energized, etc.

The energize / de-energize cycle happens so quickly you get a buzz.

On the top of the relay contacts there is a thin metal resonator with the “44” stamp that resonates that shrill tone that is heard as the buzzer.