1973 seat belt warning system logic

[RocketSurgeon]

Who knows exactly how the warning system works?
How does the neutral switch factor in?
Should the buzzer and light come on even in neutral?
Does the light come on when the key is left in the ignition and the door is opened? Or is it just the buzzer warning?
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69 Westy

[TK-CS]

[ashman40]

Here is the '73 STD Beetle wiring diagram:

Look at track 27 & 28 for the Seat Belt warning light (K19). It has four connections:

#15 = 12v+ from ignition switch
#50 = Transmission (neutral?) switch
G = Seat and seat belt switches
#86 = Door buzzer ground

The #15 is the 12v+ power source for the red lamp.
G senses when someone is in a seat but doesn't have their seat belt fastened.
#50 senses when the transmission is in gear/neutral.
#86 sends a ground to the buzzer which will buzz while the ignition is ON.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[RocketSurgeon]

What I would like to know is what is going on inside of K19.

So at the moment my light comes on as buzzes but moving the shifter does nothing. Putting the belt on turns it off.

I’ll more than likely need a replacement K19 or copy the circuit with new parts.
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69 Westy

[ashman40]

Here's the page from the '73 Owner's Manual that describes how the seat belt warning system works:

I would test both the seat belt wire (G) and the transmission wire (#50) for ground in different conditions. My guess from the diagram...

Ignition switch provides power to the #15 when in the ON/RUN position. This energizes the warning system. So the system is OFF when the ignition switch is OFF.

When the #50 wire is grounded by the transmission (presumably while in gear?) it energizes the coil which closes the contacts between G and #86. This by itself doesn't set off the buzzer.

If G is grounded while coil is energized it passes this ground to #86 which will cause the buzzer to sound. It may also ground the warning lamp turning it ON.

Just a note, if the coil pictured in the warning lamp is energized every time the transmission is in gear and de-energized when in neutral it has probably gone thru thousands of cycles in the last 40+ years. It would not surprise me if it has failed from wear.
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AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[RocketSurgeon]

Thanks for the help ashman, I guess I should have checked the manual haha! It’s all resistors and transistors In there. Not just a simple relay unfortunately.
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69 Westy

[michael svensson]

hello! this is the first time for me to post a question at the samba, so bear with me
im doing the wiring all new on my 1974 ghia convertible, and i'm a little stucked with the seat belt warning system... i'm trying to find the switch/sensor for neutral at the transaxle.. (F15 in the diagram) where is it physically placed? is there a VW part number for it? i have restored the original transaxle but couldn't find anything on it (back up light switch only).


hope that there is anyone here that can help out! thanks//michael

[Bruce]

Not all cars had the switch.
Here's where it is in the nose cone on the left side:

Then a shot of it in the car:

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