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.

[friethmiller]

Great thread, Phil. (IMG:style_emoticons/default/popcorn[1].gif) On my red '74 I rewired everything based on the following diagram (Jeff's?). I never plugged any of the "relays" in to even test it out. I wonder if it would work? This thread has me thinking. I know the passenger seat has the wiring (IMG:style_emoticons/default/idea.gif)

I know I have the smaller relay (see arrow). Not sure about the big one. I remember it being pretty bad inside.

[Superhawk996]

I know I have the smaller relay (see arrow). Not sure about the big one. I remember it being pretty bad inside.

(IMG:style_emoticons/default/biggrin.gif) good catch!

Jeff has shared that wiring info and small conventional cube relay with me. We haven’t quite figured out how what plays into this - the cube relay appears to be undocumented in any of the Haynes or factory wiring diagrams

I’m sure I’ll be asking for help from some folks to verify wiring on that - my car is a 73’.

I’ve decided to ignore the cube relay in the short term and just document the interlock relay 1st. Once that is documented - then I think we can better figure out what the cube relay is doing.

[barefoot]

I know I have the smaller relay (see arrow). Not sure about the big one. I remember it being pretty bad inside.

(IMG:style_emoticons/default/biggrin.gif) good catch!

Jeff has shared that wiring info and small conventional cube relay with me. We haven’t quite figured out how what plays into this - the cube relay appears to be undocumented in any of the Haynes or factory wiring diagrams

I’m sure I’ll be asking for help from some folks to verify wiring on that - my car is a 73’.

I’ve decided to ignore the cube relay in the short term and just document the interlock relay 1st. Once that is documented - then I think we can better figure out what the cube relay is doing.

I’ve got to apologize in advance - have some commitments with the wife that I have to take care of during the day - will try to post the cushion and belt latch info later tonight

You must have a lot of free time on your hands, is this a retirement project ? (IMG:style_emoticons/default/stirthepot.gif)
A lot of work for a tiny return to the 914 community.
Barefoot

[Superhawk996]

You must have a lot of free time on your hands, is this a retirement project ? (IMG:style_emoticons/default/stirthepot.gif)
A lot of work for a tiny return to the 914 community.
Barefoot

Yup. Personal enrichment - want to understand it and how it works. I mentioned I had character flaws right up front (IMG:style_emoticons/default/happy11.gif)

Stated as a challenge from another member that shares a hatred of the buzzer but doesn’t want to disable and bypass the Fasten Seat Belt light functionality completely.

[ClayPerrine]

You must have a lot of free time on your hands, is this a retirement project ? (IMG:style_emoticons/default/stirthepot.gif)
A lot of work for a tiny return to the 914 community.
Barefoot

Yup. Personal enrichment - want to understand it and how it works. I mentioned I had character flaws right up front (IMG:style_emoticons/default/happy11.gif)

Stated as a challenge from another member that shares a hatred of the buzzer but doesn’t want to disable and bypass the Fasten Seat Belt light functionality completely.

I would just build a small electronic circuit with a 555 timer that would turn the light on when the ignition was switched on, and shut of 15 seconds later. Then wire it to the back of the light.

(IMG:http://www.914world.com/bbs2/uploads_offsite/www.circuits-diy.com-1143-1747428580.1.png)


Replace the resistor and the buzzer with the fasten seat belt light. Instead of the push button switch, wire it to fuse 9 on the fuse box.

Now the light comes on, but no buzzer and no failed starts due to the interlock relay.

[Superhawk996]

I would just build a small electronic circuit with a 555 timer that would turn the light on when the ignition was switched on, and shut of 15 seconds later.

You did catch the part about my personality flaws right?

Ultimately I want to get to a complete schematic of the interlock relay and want to be able to model it in LTspice

Getting a bit ahead of myself but enjoy!


Why do it the easy way? Someone needs to document this thing. This whole 70s era Rube Goldberg contraption could be replaced in about an hour with an Arduino - where’s the challenge in that? (IMG:style_emoticons/default/av-943.gif)