Brake Warning Light

[lsilverman11]

Hello,

I recently finished my new wiring harness on my 1970 Bus. Brake warning light is now on whenever the ignition is on. Is this more likely to be an actual problem with my brake system? Or something I screwed up in the wiring?

Thanks,
Larry

[kreemoweet]

The only actual brake problem that could cause that would be a stuck-on brake light switch.
Assuming you have stock system with 2 3-terminal brake light switches.
The only unambiguous part of the '70 wiring diagram is at the warning light in the dash.
There, brown ground wire connects to middle terminal, which is part of removable bulb holder.
Black wire (switched power from ignition switch) goes to terminal 15 on warning light.
Red wire from switches at m/c goes to terminal K on warning light.
The terminal labels are tiny as can be, but they are there.
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[pioneer1]

Low fluid in the reservoir triggers the light....or do you mean emergency brake lite.?
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[kreemoweet]

[aeromech]

Remove your warning module and send it to Telford Dorr. You’ll get a good one back in return mail
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[Willin]

Hi
Recently, the brake warning light in my 73, is on all the time.( Engine running)
Checked grounds, checked connections to the MC, and warning light, no fluid leaks, alt. charging normally, all other lights function normally.
Brakes work normally.
Is the above advice from Aeromech my next step?
A quick search of several sellers turned up blank for these.
Can I drive without the light as may be?
Thank you!

[busdaddy]

Try unplugging one of the brake light switches, if that does nothing plug it back in and unplug the other.

This assumes you have confirmed both front and rear hydraulic circuits are actually funtional.
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[Willin]

BD
I just tried this, and there is no change. Light on dash still glows.
This happened on a re-start, half way through a 100 mile drive.
Brakes and brake lights work as they should.
I am not real clear on how the warning light works. But it sounds like the units go bad. Mine is 50 years and 24 days old @.

[busdaddy]

[Willin]

All dash lights work as they should. Checked alt. voltage at the battery, all good.
Starting bus is no problem, lights right up at the turn of the key.

[telford dorr]

here's whats inside your brake warning light:

As you can see, there's not much to it. When the brake switches apply 12 volts to the 'K' terminal, the light illuminates. When you press the indicator, an internal switch sends 12 volts from the 15 terminal to the light and it illuminates. The diode D1 prevents power from pressing the indicator from backfeeding to the brake switches, and causing the brake lights to illuminate.

If you were to swap the 'K' and 15 wires, the indicator would light all the time, so check for this.
_________________
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'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
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Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[Willin]

Thank you!

I am looking at my warning light. Part #113 919 233 B, four wires. Late,9-73 bus. No "push to test"

61-blue
31- brown- grd
15- black- 12v
K-red
That seems correct according to the w. diagram.

Module is in good shape, wire connections look good.
With a diode, current passes in one direction. Correct?
So, a test light should turn on one way, but not the other?
Could this be the issue?
Which two terminals on my light should I check? Is that the right way to do it?

Again, this problem just started recently. Warning light on (with ignition on ) all the time. All else appears normal.
The OP was the only post( I searched ) I saw that the light was on all the time. Aeromech suggested you rebuild these. Still the case?

[telford dorr]

Here's your indicator:

It's a little different than the previous indicator: the center pin (15) is 12 volts from the ignition switch fuses instead of ground; ground is pin 31. The 'K' terminal goes to the brake light switches. When it has 12 volts applied, the transistor turns on, illuminating the light. Pin 61 goes to the parking brake switch. When it is grounded, diode D2 turns on the light. Diode D1 tries to protect the transistor if you hook it up wrong.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[Willin]

Ok
But my bus doesn't have a parking brake switch.
What should I check next?

Thank you!

[telford dorr]

- Make sure that there's no connection to the indicator 61 terminal. If there is, remove it and see if the problem goes away.

- Unplug the 'K' wire. If the light stays on, the problem is the indicator (which is repairable). Otherwise, it's in the brake switches or wiring from them.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[Willin]

Hi
The blue wire in my bus goes to the blue wire at the VR. I unplugged it at the indicator and light stays on. I have a fuel pump relay wired to the blue at the VR, unplugged the relay, and indicator light stays on.
Checked voltage on K ,and got zero. Unplugged K and light stays on
Checked voltage at 15, black, and got 14.4 running.
I will add that when the key is turned to on, warning light shines bright. When engine is running light glows dimmer.

So is the indicator bad?

Thank you!

[telford dorr]

[Willin]

I will check the voltage at the blue wire and see how it compares to the black.

I looked for these units at several retailers, a quick search found none. Are these available new? " Brake warning light" -what else would it be called?
I think

If I pull the indicator and send it to you, can I still drive the bus? Mask off the loose wire ends with tape?

Do we contact you through your website?

Thanks for helping( us all ) out! I admit I'm not good at electrical,(or computers), but I have a little more understanding of this.

Another question: Can you explain how this light detects a brake problem? If, say, a rubber brake hose fails, and there is a pressure loss when the brakes are applied. How does the light know that?

[airschooled]

[telford dorr]

Yes, you can still drive the bus. Just position/insulate the wires so they can't short to anything.
For repair, send me a PM.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)