Elect Assistance - Seat Belt Delay Relay

[Black2002]

Not an E. engineer! 

Relay is '76....

Tell me I'm right or wrong......Does this relay stay open and then close in say 5 sec. or opposite? 

I've been staring at the diagram and it doesn't make sense.

It appears, the closed circuit provides a ground to all thats connected.

I thought it starts "fasten SB" light .....then goes off.

 

15 is br - ground 

31 is power from fuse 12

B, S, L all provide the  - Ground Side to Red Warning Light the "HandBrake Light"

B - Brake Fluid Level

      Brake Proportioning Circuit

      Ign Swtch -DashBoard Light !

S - Seat Belt Light - On - Then Time Delay turns off (?) (The Capacitor)

L - SeatBelt Buzzer On until tab in Seatbelt (Switch Normally Closed) interrupts circuit - making buzzer go off and SeatBelt Light Go off.

 

Somebody......help me!

 

Thanks in advace

[AustrianVespaGuy]

I believe the relay closes for the ~5 seconds when first powered up and then opens again.  When closed it provides the ground path for all that stuff (light, buzzer, etc.).  Here's how I read it as working:

#31 provides +12V to the relay coil (little rectangle with the slash in it).

Other side of the coil is connected to the bigger rectangle, which is some sort of little analog timer circuit (likely contains that big capacitor, but exactly how this works isn't specified on that diagram).  This rectangle 'allows' this side of the coil to be connected to ground (via #15) for those 5 seconds when +12V is applied to it (via #31).  It then 'disconnects' the coil from ground.

So when the coil is energized with the +12V on one side and the other grounded via that little circuit, the relay closes, and when it's closed that grounds those devices (light, buzzer, etc.) via #15.

 

P.S. Not judging, but just a little curious that you seem bent on getting this working. Most of that wiring/components I pulled out of my car a LONG time ago, both to remove the annoyance and to clean up some of the wiring/under dash space a bit!

Edited September 8, 2020 by AustrianVespaGuy

[Black2002]

I've spent way t o o much time on a restoration, to start with. (sourcing 45 year old air for the tires, etc.)

 

I've got one relay that clicks and stays that way( the subject of the capacitor replacement, where photo was lifted) Then, I have a ebay purchase that doesn' t do squat, thank you very much $30. later.

 

So I started to look at automotive timer circuits, ones that  open and one's that close, to see if they could work......not finding an available Bosch replacement.

 

I admit I fell down the rabbit hole.

 

I started questioning why not have all the ground circuits connected, it's for low brake fluid, front vs. rear brake circuit.

It seems only   relay  for the "fasten seat belt" 5 sec. notice is desirable.

 

C. It's more to think about than which TV episode, I'm up to.

 

Thanks for the reply. But am I wrong......about the grounding???

 

[ray_]

Here's a rabbit hole

 

https://www.amazon.com/s?k=timer+relay+12v&ref=nb_sb_noss_1

[AustrianVespaGuy]

1 hour ago, Black2002 said:

But am I wrong......about the grounding???

Sorry, how do you mean? The relay definitely grounds those B/S/L contacts to 'activate' those components, but the 'other' side of all those things also need their +12V supply for them to work. There's diodes in all those lines to keep them isolated from one another, so they can also be grounded separately elsewhere. For example, the BR/BL wires at the B terminal are ALL different ground paths for the dashboard 'Brake' light.  That light always has +12V when the car is on but it only lights up when grounded by one of those wires, e.g: A.) the brake level float, B.) the handbrake switch, or C.) when this silly seat belt timer relay is closed.  Now WHY the brake light is supposed to illuminate for 5 seconds when you first turn the car on is beyond me (maybe a bulb check so you're 'warned' when that bulb dies?) but that's most definitely what it does. . . Does that answer your question?

[Black2002]

Thanks for hanging with me AVG....My real question, is: not finding a timer relay.....can't I ground B, L, and S.... each of the functions turn on a light with some switch. So the relay has two jobs....seat belt for 5 sec. separately (and unecessarily) the relay closes the grounding circuit of the warnings, until a switch is tripped. ie...brake fluid goes low and closes the circuit, pres. balance, etc.

Again, my question is: can't I just ground those circuits and forget about seatbelt notice with no relay.

(diodes...? ...wouldn't they show.......like you said...it's not power we're talking about it's grounding..........and switches. 

Thanks in advance for the thoughts.

 

 

https://www.carbuilder.com/uk/. <---------rabbit hole, too..... great resource

 

[AustrianVespaGuy]

35 minutes ago, Black2002 said:

my question is: can't I just ground those circuits and forget about seatbelt notice with no relay.

So the answer to this is yes, and in fact that's how it all still works AFTER those first 5 seconds are up and the relay is open/off.  I'll break it down for you though to make sure you've got it. The dash brake light, seat belt light, and seat belt buzzer all ground-triggered circuits.  That is, they all get +12V supplied when the car is on, but then they only get turned 'on' when the other side of their circuit is grounded.  

We'll take the dash brake light as an example, because it's the most complex:

One side of the bulb in the dash gets +12V from the green/white wire that plugs into the back of the instrument cluster.

The other side of the bulb is connected to the brown/blue wires.  These wires go three places:

    A.) The brake fluid level and balance switches.  If either of these closes, the wire gets grounded, and the light lights up.

    B.) The hand brake switch.  If the handbrake lever is pulled up, the switch closes, the wire gets grounded, and the light lights up.

    C.) This timer relay.  When the timer is actuated, the relay closes, the wire gets grounded, and the light lights up.

So even if you remove the relay, the other switches still provide paths to ground and light the dash bulb.

Similarly, if you remove the relay, the seat belt light will stay off unless/until you ground the yellow/brown wire.  It will light up only whenever this wire is connected to ground.  The buzzer also works this way, e.g. will buzz only when the brown/white wire is grounded, but notice here is the additional complication of the seat belt switch (106).  This switch interrupts that ground path, so we need to have BOTH the seat belt switch closed (i.e. not buckled in), AND the brown/white wire grounded to make the buzzer sound.  Plugging in the seat belt opens this switch and breaks the circuit.

All make sense now?

[John76]

On 9/8/2020 at 4:08 PM, Black2002 said:

Does this relay stay open and then close in say 5 sec. or opposite? 

I've been staring at the diagram and it doesn't make sense.

 

The relay is closed when the ignition is on. This grounds the lights for approx. 5 sec. The time is controlled by the capacitor (the blue Radio Shack part in my original picture). 

Here's the diagram I made of the circuit. Hopefully this will aid in determining which parts you want to keep or delete (buzzer, EGR/Reactor Service box, etc.).

 

[ray_]

6 minutes ago, John76 said:

 

 

 

I want that on a t shirt.

?

[Jimmy]

27 minutes ago, ray_ said:

I want that on a t shirt.

?

 

Me too!

[Jimmy]

35 minutes ago, John76 said:

 

The relay is closed when the ignition is on. This grounds the lights for approx. 5 sec. The time is controlled by the capacitor (the blue Radio Shack part in my original picture). 

Here's the diagram I made of the circuit. Hopefully this will aid in determining which parts you want to keep or delete (buzzer, EGR/Reactor Service box, etc.).

 

 

This is awesome. Thank you for doing it and sharing. I don't think people who are good at this sort of thing realize how much those of us who aren't appreciate it.

[AustrianVespaGuy]

My big question still stands though, WHY does the timer relay also turn on the brake warning light? Just as a safety check so that you know the bulb is working?

[ray_]

1 hour ago, AustrianVespaGuy said:

My big question still stands though, WHY does the timer relay also turn on the brake warning light? Just as a safety check so that you know the bulb is working?

That's very plausible. 

 

The check control panel on my E24 is designed to show the brake light warning at start up, until you tap the pedal and confirm to it that the brake lights work...

[Black2002]

You guys ROCK..! Thanks .x 1M..and I'll sign up for the T-Shirt, too!

 

What's killing me, and I have to ask....so you can jump in and kill me, first....BUT

 

DC Circ. was taught to me , put your finger on it and trace it and don't pick finger up...and you have circuit.

 

What I don't see ....is where any of that grounds w.o. the relay?  i.e. w.o. #31...where's the ground connection?

 

I promise......my last question.

 

AVG: Timer relay and BSL: my thought, it is the early equivalent to our modern "!" light. ie "there's something to pay attention to".....in the relay's case, fasten seat belt. (This is the backdrop of '74 &'75...where car wouldn't start w.o. seatbelt if memory serves.....it's a no wonder wiring was pulled out !

 

You Guys have been great! Thanks for a welcome distraction

 

 

[John76]

5 hours ago, AustrianVespaGuy said:

WHY does the timer relay also turn on the brake warning light?

 

The reason is the power to the brake light comes from the instrument panel (specifically pin #5), which is energized when the ignition is on.  The seat belt timer relay grounds the Brake light, EGR, Seat Belt and Reactor lights (B and S tabs) momentarily through the 31 tab and all these lights come on. Even if the hand brake is off .  As soon as the capacitor discharges, all circuits are ungrounded and the lights go off....unless the hand brake is on, the brake fluid is low, and/or the EGR and/or Reactor service switch has gone 25K miles since the last reset.