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  #1  
Old 03-07-2012, 06:32 PM
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'84 W123 Seatbelt Warning Buzzer/Light

Hello Gentlemen,

Is there a way to deactivate/re-activate the seatbelt warning light and buzzer in a 1984 w123?

I'm not talking about disconnecting or unplugging the harness but I'm asking if there are ways or series of sequences/procedures, like turning the ignition key to ON position, buckle and unbuckle 3 times as soon as the warning light and buzzer shuts off etc. etc.......?

The car that I have right now, for some reason is deactivated.... the warning light and buzzer comes on when the key is turned during start-up but it does not come on anymore when the car is moving and the seatbelt is NOT buckled/fasten..... I have a high-schooler who's going to drive the car and I want to activate the seatbelt warning feature/system.

Thanks!

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  #2  
Old 03-07-2012, 07:12 PM
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None of my cars buzz if the seatbelt is NOT fastened. They'll buzz as you describe though.

With a bit of wiring work, I bet you could make it work as you describe.
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  #3  
Old 03-07-2012, 08:59 PM
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Wire it up so the engine will not start unless the belt is connected. also maybe install some type of pressure switch in the passenger seat bottom, so if he has a passenger that belt has to also be fastened to start the engine.

On our John Deere Tractor, if the PTO is on, there is a switch in the seat. If the operator gets out of the seat, it turns off the PTO. this is a safety thing.

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Old 03-07-2012, 09:26 PM
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It wasn't until the 2003 model year that cars started getting seatbelt chimes that kept chiming when the car is moving. There is no song and dance to change it... the buzzer module is fairly simple.

The one in your car sounds like its working properly. It will only buzz when the key is first turned, and then only if the seatbelt is unhooked.

I suppose you could re-wire the system to buzz all the time the seatbelt is unhooked.

-J
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  #5  
Old 03-07-2012, 10:32 PM
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Quote:
Originally Posted by compu_85 View Post
It wasn't until the 2003 model year that cars started getting seatbelt chimes that kept chiming when the car is moving. There is no song and dance to change it... the buzzer module is fairly simple.

The one in your car sounds like its working properly. It will only buzz when the key is first turned, and then only if the seatbelt is unhooked.

I suppose you could re-wire the system to buzz all the time the seatbelt is unhooked.

-J
Thanks for the info but I'm going to do a little search because I remember seing a YouTube video of a W123 where the seatbelt warning started buzzing as soon as the car started accelerating with the driver's seatbelt unfastened.
I'll post it as soon as I find it.
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Old 03-07-2012, 10:35 PM
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Quote:
Originally Posted by compu_85 View Post
It wasn't until the 2003 model year that cars started getting seatbelt chimes that kept chiming when the car is moving. There is no song and dance to change it... the buzzer module is fairly simple.

The one in your car sounds like its working properly. It will only buzz when the key is first turned, and then only if the seatbelt is unhooked.

I suppose you could re-wire the system to buzz all the time the seatbelt is unhooked.

-J
Here it is.....

1985 Mercedes 300D 0-60 - YouTube

What do you think?
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  #7  
Old 03-08-2012, 08:48 AM
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I think Tyler's was broken. They'll do that if there are grounding problems.

Check out the FSM's info on the warning system: http://eva2.homeip.net/w126-1/Program/Chassis/54-410.pdf

-J
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  #8  
Old 03-09-2012, 01:38 PM
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Quote:
Originally Posted by compu_85 View Post
I think Tyler's was broken. They'll do that if there are grounding problems.

Check out the FSM's info on the warning system: http://eva2.homeip.net/w126-1/Program/Chassis/54-410.pdf

-J
If that's the case, I guees I'll just have to figure out how to hack and create a grounding problem around the wiring or in the warning module itself, if I still want the system to work the same as in the video.

It appears that the warning buzzer and light is triggered by the speedometer. It looks like it came on @ around 3 - 5 mph..... or it's more like when he stepped on the brake pedal (but when he shifted the gear from P to D, his foot shoud have been on the brakes in the first place....)

The FSM diagram that you've attached will be very helpful. Thanks J!
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Old 03-09-2012, 02:16 PM
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Like I said, I've seen that happen in W123s with grounding problems.

You could probably use a relay and buzzer from radio shack to accomplish what you want.

I guess I'm fairly industrious... I always wear my seatbelt; but if my car had a buzzer that buzzed every time the buckle wasn't fastened it would get disabled so fast... possibly even smashed with a hammer. In fact that was one of the first things I did to my father's 2004 Passat... turn off the constant seatbelt chimer. He and I both always wear our belt and we still found it very annoying! Same thing in my friends 2003 F350.

IMHO if you want your kid to wear his seatbelt have him watch crash test videos

Actually I have an important question for you: Is this the 85 listed in your signature or an 84 as your original post said? Some 85 W123s have RS pretensioned seatbelts, and the computer looks at the buckle to know if it can activate the system. If the buckle says RS on it do not modify any wiring!

-J
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  #10  
Old 03-15-2012, 04:33 PM
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Quote:
Originally Posted by compu_85 View Post
Like I said, I've seen that happen in W123s with grounding problems.

You could probably use a relay and buzzer from radio shack to accomplish what you want.

I guess I'm fairly industrious... I always wear my seatbelt; but if my car had a buzzer that buzzed every time the buckle wasn't fastened it would get disabled so fast... possibly even smashed with a hammer. In fact that was one of the first things I did to my father's 2004 Passat... turn off the constant seatbelt chimer. He and I both always wear our belt and we still found it very annoying! Same thing in my friends 2003 F350.

IMHO if you want your kid to wear his seatbelt have him watch crash test videos

Actually I have an important question for you: Is this the 85 listed in your signature or an 84 as your original post said? Some 85 W123s have RS pretensioned seatbelts, and the computer looks at the buckle to know if it can activate the system. If the buckle says RS on it do not modify any wiring!

-J
Yea, I know that feeling of wanting to smash 'em with the hammer, my Subaru does the same thing and it's really annoying when a car is trying to be a "smart-ss" telling me to fasten up. I guess it's supposed to be that annoying for it to work and not to be taken for granted or ignored and do it's job.

To answer your question, it is a 1984, and a different car which my cousin purchased last December for his son. I'm gonna ask him if there is an RS in the buckle as my '85 does (there are similarities between '84 and '85).

We just think that the buzzer is a more pro-active safety measure to ensure that the driver wears and fasten his seatbelt everytime the car moves....you know, teens....
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Old 03-15-2012, 07:15 PM
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IIRC RS seatbelts in W123s were for 1985.

-J
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  #12  
Old 03-15-2012, 07:41 PM
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I thought the two wire connection under the seat (that are always disconnected) was for the seat belt alarm. HMmm
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Old 03-15-2012, 09:55 PM
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Originally Posted by StaggerLee View Post
I thought the two wire connection under the seat (that are always disconnected) was for the seat belt alarm. HMmm


I think from the OP, it's connected and working correctly. I think the light will come on regardless of connection and the buzzer will buzz if the belt is not connected; but it will go out upon closing the buckle or time out of the circuit.

If the buzzer is going off with the buckle closed PRIOR to start, that probably means there's wear in the buckle and it's not sensing the buckle.

If you want a continous chime when the car is in RUN and the buckle isn't closed, you'd have to cobble together a circuit - the other posters are right, there's no OE continuous warning. You could do it though, basically with a changeover relay, a warning chime and some wires.

If you wanted to get diabolical, you could wire it so the radio wouldn't run unless the belt was buckled, so he can't turn it up to drown out the chime. Both of these assume a functioning buckle switch, since you're basically hijacking its function.

See the drawing for OE functioning. Upon turning the key from OFF to RUN or START, the timer gets +12. It routes it to the seatbelt light and the seat belt switch. If the belt is undone, the switch is closed, so the +12v goes to the buzzer. If the belt is buckled, the switch is open, no +12v to the buzzer. When the timer times out, no more +12v to the buzzer OR the light. (Unless there's some other condition with the key or lights that trigger the buzzer, but that shouldn't happen in RUN or START, so it's not too likely.)
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File Type: pdf w123 warning buzzer.pdf (165.2 KB, 259 views)
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  #14  
Old 03-15-2012, 11:58 PM
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"the buzzer will buzz if the belt is not connected; but it will go out upon closing the buckle or time out of the circuit."

Sounds like he needs to bypass the timer so it's on until he fastens the belt.
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Old 03-16-2012, 12:47 AM
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Originally Posted by StaggerLee View Post
"the buzzer will buzz if the belt is not connected; but it will go out upon closing the buckle or time out of the circuit."

Sounds like he needs to bypass the timer so it's on until he fastens the belt.
That would be easier.

Probably disconnect under the seat, then jumper from pin 8 to the blue wire, reconnect the blacks. That should bypass the timer for the seatbelt. The light bulb is still on the timer. You could tie that in, a bit more complex, but do-able.

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