brake warning light

S3 brake warning light.

the brakes on my series seem to work fine but the pressure warning light thing seems to spend most of its time on. Is this common, coult it be a problem with the light or the switch?

The brakes are fairly new, have been bled and i can see no leaks.

pdf Land Rover Manuals | Landroverweb.com

There's a description of the brake warning system at the start of the brakes section.

if it's dual circuit look for a pair of either white or black and white cables going down to the imbalance switch down on the drivers sie of the chassis if it go's open circuit your light will come on so could be a dodgy cable or connector.

cheers pef ill have a check of them cables.
is there anythign else that it could be, apart from dodgy brakes.

There are 3 possible sensors powering the brake warning light. They are PDWA (pressure differential warning actuator) which monitors the pressure between the 2 circuits and tells you if one has failed, servo vacuum (sensor on servo diaphragm case) and excessive pedal travel - second switch on top of brake pedal box.)

Prior to 1980 any one or more of the 3 can be fitted - and all must be satisfactory for the light to go off. These vehicles have the warning light mounted on the test switch. A break in the wiring will put the light on.

After 1980 only the PDWA is used - with a square warning light with Brake Warning or something similar written on it. This is supposed to illuminate when the engine is started - which requires a relay on diesels which kill everything else when starting.

The PDWA is a shuttle valve and needs to be reset if it has operated. If one circuit collapses the shuttle moves. Its returned after repair by depressurising the other circuit - by loosening a bleed nipple and operating the brakes.

cheers secondjeremy, very informative answer, i will get to looking at that very soon.

SecondJeremy said:

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A break in the wiring will put the light on.

Click to expand...

Not quite, a break in the wire will stop the light lighting up at all: including when you press the switch. That's the purpose the switch - to test that the wire ain't broke. You should press it periodically to test...

I odnt think i have a switch to test it. ahh well i will check it all out soon.

The earlier system has a switch with a light for test purposes. Press switch - light comes on and goes out when released.

Later system is self - checking and has a square light only.

On the diesel vehicle the light is to indicate low vacuum in the Servo, but the switches on the servo are always at fault, I changed my many times but they only lasted a few months. You soon know if you have low vacuum as the brake pedal goes hard and the brakes feel like they are not going to stop you. I took one of the leads of the switch, light out, cured!

Is there a wiring diagram for this set up at all?