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Brake Test Switch


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#1 Disco Dan

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Posted 02 March 2009 - 02:41 AM

Today I decided to get my brake test light switch working so have written this FAQ:

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There seems to be a lot of people asking about this light/switch so hopefully people can be pointed here!

This is based on 1982 Australian assembled 998cc mini - however the all aspects should apply to other countries.

The system consists of a brake fluid level switch incorporated into the brake master cylinder cap and a dashboard switch with warning light. When your fluid level drops too low (adjustable) the red light comes on inside the switch on the dashboard to warn you. Manual states, pull over/stop asap and rectify before driving if this happens. The switch is meant to have a test function - press the switch and if the system is working correctly the light should illuminate. The switch is a self returning sprung rocker with light.


First of all, I inspected the fluid filler cap to find the metal tags inside have corroded away to nothing. I rebuilt the switch using a left over CV boot clip - perfect width and easily bent to shape. Following pictures shows the cap after being repaired:


Lever off the top with a flat head screwdriver:
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New contacts:
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Shows float:
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The switch works using a float with a brass disc that touches the tabs when the fluid level drops.

Next step was the switch and the wiring in the car.

Using a test meter and bit of luck I was able to identify the wires. I used more of the CV boot clip to simulate the fluid switch being 'on' and giving me a complete circuit for the lamp inside the car:


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The wires attached to the back of the switch:
Pink fly wire is positive feed, black fly wire is direct from brake switch. Two connector block contacts are earth and direct line from brake switch.

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Inside the switch with the front removed showing the bulb and connections.


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Back half of the switch:

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My rather crude diagram of where the wires go according to MY tests. This does not give me a working test switch - when the fluid runs low, you have to push the switch down for the light to turn on! If the fluid is fine, pushing the switch does not light the bulb. To fix this I turned the white block+spring around (Fig 8), making the switch permanently 'on' - this means I cannot 'test' the system using the button as it does not move. A better way I have now of testing the system is on the master cylinder (Fig 4) using the small 'dimple' in the centre of the cap, pushing it in simulates loss of fluid and turns the warning light on.

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If you see this your in trouble!!!

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Edited by Disco Dan, 03 March 2009 - 02:50 AM.


#2 Disco Dan

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Posted 02 March 2009 - 06:05 AM

...also good to note:

The tabs you can see in the second picture - they can be bent upwards a bit if you wish, this will make the switch more sensitive and come on sooner (very little fluid loss to turn on warning light).

Mods: make this a sticky please!

#3 Disco Dan

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Posted 02 March 2009 - 06:29 AM

Reference images for wires:

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#4 Disco Dan

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Posted 02 March 2009 - 02:45 PM

Just a quick note:

Most likely cause of the contacts 'disappearing' would be over filling the master cylinder with brake fluid. This would cause the contacts of the switch to become submerged in fluid and electrolysis will literally dissolve the contacts.

#5 DannyTip

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Posted 02 June 2009 - 10:00 PM

I did all this tonight after finding my brake fluid reservoir empty :P

Everyone should definitely do this!

Thankfully a noticed my pedal was feeling low. Either way my leak and test switch are both working now.

#6 Shylos

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Posted 03 June 2009 - 08:09 AM

Thanks for the guide, I'll definitely be having a look at this. Do you just pop the switch out of the dash with a flathead or similar?

#7 chrscmbs

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Posted 11 April 2012 - 05:52 PM

Top thread! and really interesting.

Chris.

#8 Dan

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Posted 11 April 2012 - 06:46 PM

I'm a little confused as to the point of this modification. The system works fine as designed, the adapted system doesn't work as conveniently and is just as likely to fail.




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