Engineering tomorrow

[boxhead]

Stumpeater, when you say "I have got it working by removing wire"
Are you saying that the dash light is on on your car until you remove the wire?
If so then I personally would say you have wired the switch correctly, and infact the switch has been tripped, to reset the switch, it is just a simple case of removing switch and pumping brake pedal a couple of times, then refitting switch.
No fluid should come out (if it does then there is a fault inside your master cylinder).

Forgive the rough diagram.

Originally Posted by stumpeater

Thanks Lionel & Merv for posting that schematic, very handy. I have one query, on the warning switch, there are 2 pins, I assumed they were opposite sides of the switch and hooked up one to earth and the other to the warning light, but it turns out it is actually an earthing switch, and the pins are joined inside the switch body, where does the second wire go to when used on the Falcon? I've got mine working by removing the earth wire.Thanks.

[Outwest34au]

Originally Posted by boxhead

Stumpeater, when you say "I have got it working by removing wire"
Are you saying that the dash light is on on your car until you remove the wire?
If so then I personally would say you have wired the switch correctly, and infact the switch has been tripped, to reset the switch, it is just a simple case of removing switch and pumping brake pedal a couple of times, then refitting switch.
No fluid should come out (if it does then there is a fault inside your master cylinder).
Forgive the rough diagram.

Thats what it is folks, say it 3 times slow or quick, just say it and know what it is.. "Pressure differential Switch !! Pressure differential Switch !! Pressure differential Switch !! " Thats what she said.
If you blow a hose or run short of fluid and the MC starts to pump air because your fluid evaporated for whatever reason, including worn pads and caliper pistons well extended and hence consuming all available fluid reservoir , too small reservoir, maybe a blown primary seal in the MC or whatever then the piston which is centred by a (relatively) light spring and balanced hydraulic force is displaced and a ramp activates the simple switch to mostly go to earth. This sparks up the dash lamp indicating brake fail or it is possible to have the handbrake and brake fail lamp connected so that either/ or will activate the lamp and having the ISO pic with brackets and exclamation mark (!) or similar is OK, but check with your approving person or locality.

Many people never think of the poor cheap thingy switch, but it is there to serve us and save. As Boxy pointed out if the light is on the switch is tripped. LOOSEN the switch a few turns to reduce the pressure on the spring activated pin then pump the brakes a few times to centre it (the balance piston).
The one rule that is rarely followed is,, When you bleed your brakes LOOSEN the switch a few turns, this will ensure the activation pin is not broken as the piston moves around and it will basically auto reset when the system is bled and all is balanced.

The switch is a very simple circuit that is easily forgotten about but even more easily managed. It's a PITA looking for a new switch if you break it on a sunday arvo.

Not lecturing, I just like to support the little bits that work for us.

Gary.
(spokesperson for often forgotten and neglected and mistreated parts)

[byroncobra]

Stumpy
I was scratching my head over the switch as well, on all the time, until i realised the 2 poles are connected inside.
The solution........the switch earths through the mastercylinder, so you only need a single wire returning to the dash lamp, ie 12v ign supply to the lamp, then the earth running from other side of lamp to either pole on the switch. When the plunger is pushed in by the piston (as per Gary's eloquent description) it completes the circuit and on goes the lamp.