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Jonny Hart

Resetting the Brake warning light

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Hi,

 

I recently replaced both the brake light switches and now my brake lights work BEFORE I've stopped which is a bonus. I lost a bit of fluid and I'm guessing that caused the brake warning light to come on.

 

Have tried the recommeded battery disconnect with ignition on/off you name it. Can't get the thing to go out!

 

Any other tricks?

Edited by Jonny Hart

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If you lost some brake fluid then could there be an air bubble in the system, trapping some fluid pressure against a sensor????

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If you lost some brake fluid then could there be an air bubble in the system, trapping some fluid pressure against a sensor????

 

only lost enough to take it just below the level. will test the switch in the cap but think there is more to it than just that.

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Hi,

 

I recently replaced both the brake light switches and now my brake lights work BEFORE I've stopped which is a bonus. I lost a bit of fluid and I'm guessing that caused the brake warning light to come on.

 

Have tried the recommeded battery disconnect with ignition on/off you name it. Can't get the thing to go out!

 

Any other tricks?

 

Hate to suggest the obvious but do you have the wires on the right way round?

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Hate to suggest the obvious but do you have the wires on the right way round?

 

The wires on the switches are three prong so can't be misconnected. Might have them swapped front to back though. Will go check

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The wires on the switches are three prong so can't be misconnected. Might have them swapped front to back though. Will go check

 

Nope, they go to the right switches. I think that there IS a fault with the rear switch as it doesn't make the contacts when no pressure is applied (although it does work the brake lights ok on its own).

The front one works ok in both positions.

 

I understand that the light will go on if there is a discrepancy, so I made up two links and rigged them to the connectors in the same orientation for both. battery off, reset.

 

Still can't make the light go out. But I do notice that if I rig the connectors the same, then the light takes a split second longer to come on (when compared to the park brake light) than if the connectors "disagree". I'm leaving the earth off the battery for 5 mins with the ignition "on" between tries.

 

[uPDATE. Ok, so I forgot you had to start the car - doh! Looks like one of my new pressure switches is faulty then. Funny, cos I already had one of the new ones replaced! So if the next one works that will be a 50% failure rate straight out of the box!]

Edited by Jonny Hart

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The switches are crap. I installed a mechanical switch as I was so fed up with mine and the length of time it took for them to come on. That was after changing for new ones. Lights work perfectly now and I have adjustment if I need it.

 

See here http://www.impactbumpers.com/forum/index.php?showtopic=17733

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if the brake light switches are functioning properly then the little circuit board behind the brake warning light

might be faulty. It 'monitors' both switches and if either one is 'on' while the other is 'off' then it turns on the

warning light. Mine was totally dead, but a bit of soldering and a new transistor fixed it.

Edited by steeley

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if the brake light switches are functioning properly then the little circuit board behind the brake warning light

might be faulty. It 'monitors' both switches and if either one is 'on' while the other is 'off' then it turns on the

warning light. Mine was totally dead, but a bit of soldering and a new transistor fixed it.

 

Thanks Steely but it is one of the (brand new) switches. It operates the lights ok but does not switch back when the pressure is off (hence the state is not the same as the other one) Should get a replacement today.

 

Phil. Your mod is on my to-do list. I really need to finish some other jobs first. Tackling the snakes wedding under the dash at the mo...

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Ok, I have the replacement switch and have tested with a meter that they now both work BUT I still get the warning light.

 

The terminals numbers are small but just about visible on the connector and labelled 81,81a and 82a.

 

According to the wiring diagram, the car expects the following to occur:

 

no braking - 81 and 81a are connected

under braking- 81 and 82a are connected

 

(81a is the feed to the warning switch)

 

However, the switches supplied do the following

 

no braking - 81a and 82a are connected

under braking- 81 and 82a are connected

 

Although this results in the brake lights coming on when the pedal is pressed, this triggers the brake warning light (on my SC anyway) as the circuitry expects 81 to be connected to 81a when the pedal is not pressed. I have simulated what the new switches do using wire links instead of switches and get a warning light every time.

 

I was hoping that someone could do me a big favour and post up what their switches do.

 

Also, the wiring colours to the terminals on my car don't correspond to any of the MYs shown in Haynes ( really must get the Bentley manual)

 

I have:

 

81 - black/green

81a - white/black (middle terminal)

82a - green / yellow

 

 

Help greatly appreciated.

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Have you got wear detectors on the pads?

 

No.

 

As I said, forgetting the switches for a minute, I can completely simulate this with wire links in the sockets.

 

If I simulate what the schematic seems to expect - no warning light - everything works.

If I simulate what the new switches are actually doing - warning light comes on

 

Matt (Type911) assures me that although the switches are the VAG ones, he has sold tons of them with no complaints. I don't doubt him. I am just baffled as the VAG switches don't appear to operate how the car expects them to.

 

If I reset the light, start the car with the brake pedal pressed, the warning light is off, only to come on when the pedal is released. Again, this ties in with my previous post highlighting what I believe to be a difference in the way the switch operates.

 

Maybe an OP has fiddled with my car's wiring?

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A wiring fault /PO bodge somewhere sounds possible.

 

Don't forget the fluid reservoir switch is wired into this circuit as well. Maybe something going on there.

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A wiring fault /PO bodge somewhere sounds possible.

 

Don't forget the fluid reservoir switch is wired into this circuit as well. Maybe something going on there.

 

 

As stated earlier, I can get the warning lamp to go out by applying the correct inputs using wires, but the brake switches don't work how the schematic expects them to.

 

I see you have the same year car as me. Any chance you could check the wiring colours out for me?

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Shes away in winter storage at the moment- will probably be back here end of next week.

Can check wires then for you if its not too late.

 

I see you have the same year car as me. Any chance you could check the wiring colours out for me?

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I am now pretty much convinced that the switches I have don't operate as the car expects.

 

Here is the vw schematic which shows the same circuit as the 911. At rest, the switches I have short 81a and 82a. This isn't correct and results in the warning lamp on.

 

3brake.gif

 

Matt, I don't doubt for a minute that the switches that you have previously sent out were correct, but the ones I have are not right. I want to get to the bottom of this and it could save you some hassle if you've been supplied incorrectly.

 

Do you have access to a multimeter? If so, could you sample a few switches. With terminals facing you and the central one at the top, the top and right hand terminals should be connected.

If it's the left hand terminals connected (as per the ones I have) then they won't work with the brake warning circuit.

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Sorry about this Jon

 

Just checked 2 here and they are the same as the ones you have there, ie; centre and left terminal closed. I have sold loads of these (dozens in the past year) so Im a bit stumped like you!

 

Maybe OPC is the best bet for a Genuine switch to see if there is a problem with my switches (£24 + vat though)

 

Hope you get it sorted

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Thanks Matt. Were the switches the Electrix ones? Part number?

 

Anyone with a working system care to do the same check?

Edited by Jonny Hart

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ok, just remembered I had a switch in the garage and it as per the diagram.

 

Looking at the back of this switch it meters centre and right-hand pin shorted at rest (81a and 81)

 

This particular switch is made by Euromax and came from here:

http://www.justkampers.com/shop/brake-ligh...pin-j10535.html

 

Thanks steely, that confirms that not all VW three prong switches are the same. I will order those ones you recommend.

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Interesting, let me know how you get on with this Jon, maybe I should be buying my switched from those people! (cheaper than my supplier anyhow!)

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OK, follow up to this is that I have here a brand new ATE master cylinder with the switches installed and these are different! Looks like a complete wrong batch, be careful though as these are From Dansk and they do suplly half the VW world too!

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OK, follow up to this is that I have here a brand new ATE master cylinder with the switches installed and these are different! Looks like a complete wrong batch, be careful though as these are From Dansk and they do suplly half the VW world too!

 

Good to hear that I wasn't having a senior moment. Refreshing too, that you have been upfront and open about everything from the start, Matt :ani_clapping:

 

So do you have some correct ones in yet? I didn't get round to ordering from the other place yet so could test the new ones out for you.

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I have ordered some but wont see them for about a week I would think, I will send you 2 (if you still need them, or refund you if you dont) once I have checked there are correct!!

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