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79' Super Brake Lights Quit Working
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abl1111
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PostPosted: Fri Sep 21, 2018 11:26 am    Post subject: 79' Super Brake Lights Quit Working Reply with quote

Brake lights suddenly stopped working.

Last two years replaced all brake components including switches.
All worked fine
Fuses OK
Brake light bulbs Ok
Connections behind insulation 'seems' fine - I'll check better later.
All other lights work.
Last year had headlight issue - cleaned fuse connections all worked fine again.
Drove car today and applied brakes hard a few times to see if I could 'fix' the brake switches. No effect.

Where should I check ?
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abl1111
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PostPosted: Fri Sep 21, 2018 3:57 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

Not a riveting topic. I've been checking via Search - a lot or info from many years.

In order to troubleshoot the master cylinder brake switches - is it correct to connect the 82a and 81 terminals for both switches ? Then step on the brake ? Or will they light up ( if the switch is bad ) without stepping on the brake pedal ?

If this lights up the brakes then the brake switch(es) are bad ?

And, if they still don't light up - I have an issue elsewhere - sound correct ?

If the lights still don't light up, where should I look after this test ?
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mukluk
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PostPosted: Fri Sep 21, 2018 4:19 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

Connecting the 82a (R/Y) to 81 (R/BK) together on either switch should make the brake lights illuminate when the ignition is turned on. If they don't light up, check that you're getting power in at the R/Y wires -- if you find your horn isn't working either that would indicate a poor connection at the fuse 11 output of your fuse block.

The brake lights are on circuits 38 and 41 of the diagram.
https://www.thesamba.com/vw/archives/info/wiring/76-79113wiring.jpg
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abl1111
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PostPosted: Sat Sep 22, 2018 6:11 am    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

I tested both master cylinder switches and - when I connect 82a and 81 - the brake lights work.

Does this mean there's an issue with the switches ? I always feel suspect when (2) of something that work independently, fail at the same time.

Or, an issue with the master cylinder ?

The master and both switches are relatively new - within 2 years. I forget which brand switches I bought, but originally I had installed 'any old pair' when I redid brake system and (1) of them blew out. So, I went and bought what I thought were premium, name-brand switches.

Thoughts ? and thank you.
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mukluk
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PostPosted: Sat Sep 22, 2018 11:21 am    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

Since jumpering the input and output wires gets the brake lights to work, the only explanation for them not working normally is the brake light switches are bad. Provided stepping on the pedal causes the brakes to work sufficient to stop the car and the pedal doesn't go almost to the floor, you can rule out the master cylinder as being a possible cause.
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abl1111
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PostPosted: Sat Sep 22, 2018 11:48 am    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

OK ! Been waiting to hear from you. Thanks. Brakes work great - no sponge, pedal is high !

Do you have a recommendation for quality switches for my late model super ?
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mukluk
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PostPosted: Sat Sep 22, 2018 11:56 am    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

I haven't had to buy a three prong brake switch in over two decades, so I can't say for certain who has good ones nowadays. I know in the past ATE switches were good.

113945515G Brake Switch
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abl1111
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PostPosted: Sat Sep 22, 2018 1:05 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

Just so I understand - these switches work on hydraulic pressure, right ?

Is it possible there’s an issue with mc not properly pushing fluid through to activate the switches ? Just odd that both switches went at the same time...
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PostPosted: Sat Sep 22, 2018 1:50 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

You probably only had one switch working from the start. The new switches are from CHINA and they leak and fail. Keep your eye on any new switches you put in.
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PostPosted: Sat Sep 22, 2018 2:38 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

abl1111 wrote:
Just so I understand - these switches work on hydraulic pressure, right ?

Is it possible there’s an issue with mc not properly pushing fluid through to activate the switches ? Just odd that both switches went at the same time...

The switches are hydraulically actuated, yes. Taking into account the high firm pedal and good brake performance, the likelihood that something is wrong with the master and therefore not producing sufficient pressure to activate the switches is extremely low. There is a slight possibility that by some chance both switches managed to get a bit of crud in them which is blocking the fluid from activating them, which you are more than welcome to try removing and cleaning the switches to test that theory, but it's most likely a case of both switches have failed.
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abl1111
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PostPosted: Sat Sep 22, 2018 3:10 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

OK - Thank you, I'll order a pair and report back to you.
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PostPosted: Sun Sep 23, 2018 2:56 am    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

Did you TEST the switches? No use ordering new ones if the current ones actually work.

With a multimeter set to read resistance, measure the resistance of the opposite facing male terminals of the brake switch itself (one at a time). Without brake pressure there should be infinite resistance between the opposite terminals. When you press on the brake pedal, the pressure should close the contact between the two terminals and the resistance should drop to zero. Check that BOTH switches are working.

There was some concern a few years back that the contact surfaces of the (cheap) brake switches were so small that the current flow of the brake lights (25W x2) would quickly create a burnt spot on the switch contacts and render them dead after only a short period. One solution was to add relay into the brake light circuit so the brake switch contacts would last longer. This is the same principle as adding a Hard Start Relay into the starter solenoid circuit. Here is a related article explaining why a relay may be needed and how to wire the relay in (see the diagram marked "negative ground"):
https://www.mgexp.com/article/brake-light-relay.html
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abl1111
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PostPosted: Sun Sep 23, 2018 1:05 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

Ash,

I'm electronically challenged so bear with me.

" With a multimeter set to read resistance ( ohms ), measure the resistance of the opposite facing male terminals of the brake switch itself (one at a time). I left one plug on while I measured the other switch, then changed to the other switch - Without brake pressure there should be infinite resistance between the opposite terminals. Both read "OL" When you press on the brake pedal, the pressure should close the contact between the two terminals and the resistance should drop to zero. These each had different readings, one showed 1.6 ohms, the other 71.7. Check that BOTH switches are working. "[/b]

What do these readings mean ?
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PostPosted: Sun Sep 23, 2018 2:03 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

YouTube is your friend.

https://www.youtube.com/watch?v=TdUK6RPdIrA


https://www.youtube.com/watch?v=gYJsakJo7YE
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PostPosted: Sun Sep 23, 2018 3:57 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

Try a shot of Wd 40 with bulb out of socket
Worked for mine and it kills the corrosion
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PostPosted: Sun Sep 23, 2018 6:28 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

abl1111 wrote:
Ash,

I'm electronically challenged so bear with me.

" With a multimeter set to read resistance ( ohms ), measure the resistance of the opposite facing male terminals of the brake switch itself (one at a time). I left one plug on while I measured the other switch, then changed to the other switch - Without brake pressure there should be infinite resistance between the opposite terminals. Both read "OL" When you press on the brake pedal, the pressure should close the contact between the two terminals and the resistance should drop to zero. These each had different readings, one showed 1.6 ohms, the other 71.7. Check that BOTH switches are working. "[/b]

What do these readings mean ?


It sounds like one of your brake switches may be OK and the other is definitely shot.

When you measure resistance in a circuit, basically what you are measuring is the amount of "obstruction" or resistance to the eletrical current's flow. The closer the resistance reading is to 0, the more current is being allowed to flow through the curcuit.
Take a simple strand of wire, set your meter to resistance (ohms) and put a probe at each end of the wire. You will see your meter read 0 or clse to it, becuase there is nothing obstructing the path of a current you put through that wire. (You may get a reading close to but not quite 0, like 0.03 or something--this is simply a tiny resistance due to the windings of the strands in the wire, or maybe the insulation jacket, etc. but basically the full current is being allowed to flow through the unbroken wire.) This would be a CLOSED circuit.
You can also use this method to determine whether a signal path is broken. If you keep the meter probes on either side of that wire but then cut that wire in half, your meter would suddenly read "1" or "OL" which means "Open Loop" which simply means you now have an OPEN circuit where the current cannot pass through the circuit from one point to the other.

Back to the brake switches. Take a look at this diagram from Speedy Jims website:

Image may have been reduced in size. Click image to view fullscreen.


Look at the very bottom of the diagram and you will see an illustration of the brake switches as you are facing them when installed on the master cylinder. You will see the opposing terminals of the switch that you are placing your meter probes on are the 82a and 81 terminals of those switches.
Now look at the main diagram. This diagram shows the electrical current path: current flows from the fuse box, splits into two wires and flows into terminal 82a on both switches. If the brake pedal is not being pushed (at rest) then the "gate" inside each switch is OPEN causing an open circuit in the siwtches, so that current cannot flow through and out terminal 81. When you push the brake pedal, the brake fluid inside each master cylinder circuit causes the gates inside the switches to close, thereby creating a CLOSED circuit and allowing current to pass through and out terminal 81 where they rejoin into 1 wire and go on back to your brake lights.
Now look in the upper left of the diagram in the green box. This box shows what happens when one of your brake switches fails (i.e. a loss of brake fluid pressure is causing the gate inside one switch not to close.) In this example the working switch is on the right and the non-working switch is on the left. Current still flows through from 82a to 81 on the working switch on the right, BUT instead of flowing back to the brake lights the current takes the shorter path to ground which is now "backward" through the non-working switch on the left, up to the dash warning light (which lights up) and then to ground.

Now let's go back to the readings you took on your brake switches. I suspect that the one switch that reads 1.6 ohms is still probably OK because it is farily close to a 0 reading-- at least it is letting most of the current still through when you push the brake pedal. But the other one has a resistance reading so high that it doesn't seem to be letting any current through, this would be the non-working brake switch causing your lights not to function. (This whole scenario does the beg the quesiton: Is your dash warning light lighting up??)

At any rate it would be best to go ahead and replace both brake switches with known good German brands such as the ATE brand listed above.

Hope this helps-- ashman is the real resident eletrical expert here so he will be along shortly to correct me if I got something wrong (which I always welcome!) Very Happy
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Last edited by sb001 on Mon Sep 24, 2018 7:36 am; edited 1 time in total
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PostPosted: Sun Sep 23, 2018 6:48 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

SB

WOW ! Thank you or taking the time to type that. I understood exactly what you wrote to a T. I have a basic knowledge of electrical but am not good with the voltage meter ( I own a great digital, Fluke meter to use, but am not confident with it. ).

I will take every piece of advice and apply ( WD etc ) - starting with the switches. I would like to pull them out and inspect them - try to clean them, before I replace. Is that possible ? I was thinking of buying small bolts to thread into the MC so I could minimize brake fluid leakage while I check the switches, clean, reinstall and see if that works.

Good / Bad idea ? Waste of time ? If a waste, I'll just order new ones. If not, I'll try to clean 'em ( what thread are they ? )

Lastly, if I do try to clean them, do you think an air compressor with the right fitting to create pressure on the switch would activate the switch ( to mimick hyd pressure ? )

By the way, I've owned this car for 31 years !!! A long time to have a car ( I used to have a full head of hair - not so much anymore ). I never stop learning and expanding my mechanical and technical experience - or lack of, with her !
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PostPosted: Sun Sep 23, 2018 7:09 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

Honestly I would just go ahead and buy the new switches-- as ashman mentioned earlier the problem may be burned spots on the eletrical posts inside the switch (that may explain your 1.6 ohm reading) but that other switch is shot IMO. Good German brake switches are not that expensive and you won't have to worry about it again for years

https://www.thesamba.com/vw/classifieds/detail.php?id=2159281
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PostPosted: Sun Sep 23, 2018 7:21 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

Agree w/ sb001. While the 1.6ohm switch could still be used the 71.7ohm switch is BAD. The resistance is likely caused by low quality contacts inside the switch... or, over time the contacts become carbon burnt from the current flowing thru the switch. Low quality switches will get burnt faster than better German ones.

So replacing both switches is probably you best option. Look for some good quality ones (skip the $10 switches and expect to pay closer to $25/ea).

Also, if you want to prevent the same from happening for a long time, add a relay to the circuit (see above link), or replace the stock incandescent brake bulbs with hyper-bright LEDs that only draw 2W instead of 21W. The reduced current will make the switches last longer.

FYI, the stock 21W bulbs pull around 3.5A thru the switches.
The 2W LED bulbs will pull around 0.33A.
Adding a relay to the circuit results in only about 0.050A passing thru the switches (just enough to energize the relay). If you add a capacitor and diode as shown in the link above you get a much longer life from the switches (like the life of the car long).
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PostPosted: Sun Sep 23, 2018 8:15 pm    Post subject: Re: 79' Super Brake Lights Quit Working Reply with quote

sb001 wrote:


Image may have been reduced in size. Click image to view fullscreen.




Edited my post above
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Bosch 113905205AE autostick distributor


Last edited by sb001 on Mon Sep 24, 2018 7:37 am; edited 1 time in total
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