Brake light warning

[Ringo911]

Hi IB family… I have a bit of an odd fault with my 79SC…when driving back from a short journey, my brake light warning light came on and will not turn off!!

So to give you a bit of background to what has been tried to date to fix and what I know of the system.

1. It’s the brake light warning light not the handbrake light
2. No issues before and has no problems with disc and pads are only a couple of years old, also my 79 does not have any pad wear sensors
3. Checks brake fluid level and all ok  
4. Disconnected the battery over night and light still on (this was to try and reset the x2 brake switches as act as pressure sensors to checks if both front and back master cylinders have same pressure.

 

Ok that’s the background, what I have done to try and fix…

 

• Replaced both x3 prong brake switches on master cylinder
• Tested the level swich on the fluid reservoir
• Flushed and bleed the brake fluid
• Disconnected the battery again after light still on to try and reset.

So I am now stuck as light is on consent. The only thing I was going to try was to drive it for a bit, and then try and reset by disconnected the battery again, if this doesn’t work I could really do with some help/ideas

Thanks all in advance. 😊           

[Phill]

I don't know if it's just on 3.2s but I think there is some reset procedure involving battery disconnection and the ignition key. Calling @SilverWT

Try this 

 

  For your brake warning light the theory is to turn your ignition on, disconnect your battery neg lead, leave for ten mins or so and reconnect.  It often works, but sometimes doesn’t.  

[Lesworth]

That's what I did on my SC. Ignition on, battery off, have a cup of tea, ignition off, battery on, away you go.

[Ian Comerford]

2 hours ago, Lesworth said:

That's what I did on my SC. Ignition on, battery off, have a cup of tea, ignition off, battery on, away you go.

I have the same fault on mine and this fix did not work.  I know it’s often quoted as a fix but it doesn’t always work it seems.  

[SilverWT]

18 hours ago, Phill said:

I don't know if it's just on 3.2s but I think there is some reset procedure involving battery disconnection and the ignition key. Calling @SilverWT

Try this 

 

  For your brake warning light the theory is to turn your ignition on, disconnect your battery neg lead, leave for ten mins or so and reconnect.  It often works, but sometimes doesn’t.  

It's an SC thing only, the 3.2 does not have this electronic witchcraft!

Mark

[Type911]

It might be worth taking the light unit out and see if its ok, there is a PCB in there

[Ringo911]

Thanks for the info. I did take it out and can’t see any burnt out components or dry joints on the PCB. But I have friend who has a spare that I going to try. 
if not it maybe an issue with balance in the MC. But don’t want replace just in a whim. But after trying a replacement warning light module l don’t know what else to try. 
🤨

Also, don’t know if someone can check please. On the two connectors on the break fluid cap, when checking continuity is it shown open or closed as my is closed when the cap is on and fluid full. Cheers  

[Phill]

Did you try the above method?

[Ringo911]

Hi Phil I did try the reset method but no joy. I going to borrow a warning light module and see how I get on. Also I forgot I installed LED bulbs as break light. It was a couple of years back and had no issues, but will try normal bulbs as never know. 

[Jonny Hart]

Ok. First thing to know is that all you have to do is disconnect the battery for a short period of time.  5 seconds is enough. 
 

With battery reconnected, do not touch the brake pedal and turn the ignition on. The brake warning light will be off.   If it is on in this condition, electrically disconnect the pressure switches, reset and repeat test.  If the light remains off then at least one of the switches is faulty. 
 

If the lamp stays off, but lights up as soon as you touch the pedal, then this is also a faulty switch OR the wrong switches.  
 

Note that there are 3 pin VW switches that ‘fit’ the 911 but the pin function is different.  These will result in the warning light coming on as soon as the pedal is touched.   They will also split under emergency braking resulting in complete loss of brakes.    I probably owe the MOT man my life for finding this out before I did!

Fit genuine Porsche switches   

 

Edited August 13, 2021 by Jonny Hart

[Ringo911]

Hi everyone. Firstly thanks for everyone’s help and advise. 
I think I have fixed the issues by replacing the break warning module in the dash. Luckily I found a good on eBay from a 924 same part number. Fitted took for a test drive today and still no error. The light comes on with ignition but as soon as she starts the light goes off like it should. Another gremlin bites the dust!! 😜👍🙏🏻