Brake failure light question

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ethana
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Brake failure light question

Post by ethana » Mon Feb 11, 2019 5:20 pm

The brake failure light does not come on when the ignition is first turned on (engine not running). The light works when the parking brake is applied and the alternator light behaves normally (comes on with ignition on and goes off when the engine starts. This problem is new.

Any thoughts?

stock '77 Westy
Ethan
'77 Westy

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Amskeptic
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Re: Brake failure light question

Post by Amskeptic » Mon Feb 11, 2019 6:07 pm

ethana wrote:
Mon Feb 11, 2019 5:20 pm
The brake failure light does not come on when the ignition is first turned on (engine not running). The light works when the parking brake is applied and the alternator light behaves normally (comes on with ignition on and goes off when the engine starts. This problem is new.

Any thoughts?

stock '77 Westy

Check to see if the blue #61 wire is securely attached to the brake light switch.
Great access. Easy. . . Not.
Colin
2019 Annual Funding Drive!
**********************************
viewtopic.php?f=41&t=13755

BobD - 1978 Bus . . . . . . . . . . .111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 97,179 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 77,717 miles

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ethana
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Re: Brake failure light question

Post by ethana » Tue Feb 12, 2019 5:03 pm

No blue wire. #61 has the white/green wire that goes to the parking brake (a la Bentley 1979). No other loose wires in the vicinity. When it is working how does the light "know" to turn on with the ignition and off when the engine starts?
Ethan
'77 Westy

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tommu
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Re: Brake failure light question

Post by tommu » Tue Feb 12, 2019 7:25 pm

Where are you located Ethena?

Have you caught up on this: viewtopic.php?f=78&t=13761

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ethana
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Re: Brake failure light question

Post by ethana » Wed Feb 13, 2019 5:41 pm

For sure the light does not come on with the ignition on, engine stopped, parking brake off, but will come on if I pull out the parking brake.

Right now my bigger problem is that we got about 16" of snow today with winds 20-30mph and I parked facing the wrong way, so the engine compartment filled with snow. Several inches all the way through! I couldn't see the oil filler or cooling fan! So it wouldn't start after work. It does have spark and the fuel pump runs when I push the flap in the AFM. I just bought a cheap electric heater and an extension cord and will try to dry it out tomorrow. Luckily I parked in front of the only electrical outlet on that side of the parking lot! Who would have thought that would be important...
Ethan
'77 Westy

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ethana
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Re: Brake failure light question

Post by ethana » Thu Feb 14, 2019 8:33 pm

All the wiring looks fine behind the dash board and fuse 11 is good (brake lights and horn work). Maybe the idiot light unit is bad? Anybody have a schematic for the wiring inside the brake warning light (K7 in Bentley).

I still don't understand how the light knows to turn off when the engine is running. Before looking at the Bentley I thought it used a wire from the alternator to do that. But I don't see it in the 1977 electrical diagrams.
Ethan
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Re: Brake failure light question

Post by Amskeptic » Tue Feb 19, 2019 6:25 am

ethana wrote:
Thu Feb 14, 2019 8:33 pm
All the wiring looks fine behind the dash board and fuse 11 is good (brake lights and horn work). Maybe the idiot light unit is bad? Anybody have a schematic for the wiring inside the brake warning light (K7 in Bentley).
I did not ask if Fuse #11 was good. I was informing you of two different power paths to the warning lamp.

Fuse #11 supplies ignition-on voltage to the light.
There is a "diode" that keeps ignition supply (15) voltage separate from brake failure (K) voltage. Both ground through 31 normally.

ethana wrote:
Thu Feb 14, 2019 8:33 pm
I still don't understand how the light knows to turn off when the engine is running.
And here we are . . . yes, I would replace the switch and hope that my diagnosis of a bad diode proves correct.
Colin
2019 Annual Funding Drive!
**********************************
viewtopic.php?f=41&t=13755

BobD - 1978 Bus . . . . . . . . . . .111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 97,179 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 77,717 miles

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ethana
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Re: Brake failure light question

Post by ethana » Mon Apr 08, 2019 7:46 pm

Amskeptic wrote:
Tue Feb 19, 2019 6:25 am
And here we are . . . yes, I would replace the switch and hope that my diagnosis of a bad diode proves correct.
Colin
So I changed the brake warning light unit and still same problem.

Here's a picture of it disassembled and a schematic I drew up.
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Ethan
'77 Westy

kreemoweet
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Re: Brake failure light question

Post by kreemoweet » Mon Apr 08, 2019 10:55 pm

With the change to the brake warning light wiring (which occurred with the 1976 models, according to the Bentley wiring diagrams, which substituted the parking brake switch wire
at terminal #61, instead of the previous alternator warning lite wire, the light no longer turned off when the engine started, but when the parking brake was released, and the
brake warning light no longer came on automatically when the ignition was turned on. An improvement in function, IMO. It does not seem that the OP actually has a problem, and the machine is performing as designed.

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tommu
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Re: Brake failure light question

Post by tommu » Tue Apr 09, 2019 11:00 am

I just checked my '76 brake warning light. Light comes on when ignition is on. Light stays on when engine running. Light turns off when brake disengaged.

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ethana
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Re: Brake failure light question

Post by ethana » Thu Apr 11, 2019 9:32 pm

kreemoweet wrote:
Mon Apr 08, 2019 10:55 pm
With the change to the brake warning light wiring (which occurred with the 1976 models, according to the Bentley wiring diagrams, which substituted the parking brake switch wire
at terminal #61, instead of the previous alternator warning lite wire, the light no longer turned off when the engine started, but when the parking brake was released, and the
brake warning light no longer came on automatically when the ignition was turned on. An improvement in function, IMO. It does not seem that the OP actually has a problem, and the machine is performing as designed.
Until recently (read two months ago) the light did come on with the ignition on and parking brake off and would go out when the engine started like the alternator light. This is how it should function according to the owner's manual for my '77. I agree that the Bentley wiring diagrams do not show this.

Maybe some other '77, '78, '79 owners can confirm the functioning of their brake warning lights.
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Ethan
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ethana
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Re: Brake failure light question

Post by ethana » Thu Apr 11, 2019 9:36 pm

tommu wrote:
Tue Apr 09, 2019 11:00 am
I just checked my '76 brake warning light. Light comes on when ignition is on. Light stays on when engine running. Light turns off when brake disengaged.
If you turn the ignition on and release the parking brake does the light stay on (engine not running)?
Ethan
'77 Westy

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Amskeptic
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Re: Brake failure light question

Post by Amskeptic » Fri Apr 12, 2019 7:22 am

ethana wrote:
Thu Apr 11, 2019 9:36 pm
tommu wrote:
Tue Apr 09, 2019 11:00 am
I just checked my '76 brake warning light. Light comes on when ignition is on. Light stays on when engine running. Light turns off when brake disengaged.
If you turn the ignition on and release the parking brake does the light stay on (engine not running)?

The Law demanded a driver verification of the functioning of the warning lamp.

1968-69 buses had a self-test where you pressed the lens and the light was to illuminate.
1970-75 buses had an "ignition on" test utilizing the alternator 61 ground.
1976-up buses used the applied parking brake as a light test/warning.

On my 1977 bus, ignition-on/parking brake-off, the light does *not* illuminate. The owner's manual inartfully muddles the change in function as of 1976, and does not state clearly enough that the brake warning light takes its cue from the applied parking brake only.

I may very well have led you astray, and have edited the flow of this thread to account for kreemoweet's observation that your warning light is functioning correctly.
Colin
2019 Annual Funding Drive!
**********************************
viewtopic.php?f=41&t=13755

BobD - 1978 Bus . . . . . . . . . . .111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 97,179 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 77,717 miles

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