Brake Warning Lamp Circuit

quattro said:
The only brake pad switch (bullet connector) to be live with all of the pads disconnected would be the first one that the the circuit goes to, and I'm not quite sure which one it is.

Richard
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The first one is the front RH brake so if the connection to the reservoir is live, the wire then goes directly to the bullet connectors just inside the engine bay on the Right hand side.

I must admit that my handbrake warning light doesn't work since I got rid of these wires, so I am of to the garage to check it out :)

Richard
 
Does a dual circuit UK car have two independent brake fluid reservoirs or just one? The NADA diagram is noticeably different from the UK one for brake warning light wiring!
 
harveyp6 said:
darth sidious said:
But they are in parallel on the diagram, aren't they?
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They are after the pad warning light system, but the handbrake switch should be between the last pad and earth, and the two reservoirs should have the ignition supply directly to each of them, through the switches to earth, and the pad warning light system should take its supply from the live side of one of the reservoirs. So on that illustration after the last pad the circuit should go to the handbrake switch and then to earth, not through the reservoirs. At the top of the pic there should be a split in the supply before the pads, which goes to the two reservoirs as a parallel circuit to the pads. In other words break the link between the last pad and the reservoirs, and take the supply for the reservoirs from a point before the first pad. Operating the handbrake only tests the pad warning light system, that's why checking the reservoir switches is a service item. The way it's been illustrated the handbrake switch is testing the reservoirs as well. It would be so much easier if I could draw it out ......
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I think I get your point now! What your saying, boiled down, is the fluid reservoir(s) is (are) the next "stop" after the bulb, then the front pads, then the rear pads, finally through the handbrake switch and to earth. That being, even if the wires on the pads get damaged, the reservoir's(s') connections would still light the bulb on the dashboard if the fluid level got too low. :)
 
With each component being individually earthed, the system will work all the way up to the first break in the positive supply, which should make fault finding quite straight forward, start with the reservoirs and work your way along until earthing a component doesn't turn the light on.

I'm fairly sure the main problem will be the supplys to the pads, looking at the diagrams, and from memory they have seperate in and out positive connectors, so if any one is disconnected or rotten, that will break the rest of the circuit.
 
JVY said:
I understand you Harvey :) .
testrider, If you have a multimeter you could do some quick tests that might identify the problem:-

1. At the handbrake switch, with brake off (i.e. switch open), use a mulimeter to test for +12V on the contact of the switch that is connected to the +12V live pickup on the resevoir. If you don't have meter, you can use a small 12V bulb. If there is no 12V at the handbrake switch contact with the switch open, this means you must still have a break in the wiring between the resevoir and handbrake switch.
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There is no power to the handbrake switch as it's the last thing in the circuit so the fault is further up the wires.

JVY said:
2. The other contact on the hadbrake switch should be connected to chassis. You can use a multimeter on ohms setting to check for continuity.

3, If the above tests are OK, check the continuity of the handbrake switch when closed to make sure the switch is working.
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Haven't had chance to check this yet, but I don't want to pull the interior to pieces 14 hours before the MOT. I'll do that if it fails.

JVY said:
You said there was no live (at front pad bullet connectors?) with handbrake on. You wouldn't expect to see live 12V here with the handbrake switch closed if all was working OK. However, I would epect 12V with the handbrake off (switch open).

BTW, good luck with MOT. Unless the tester is familiar with P6's my guess is he won't know about the warning light? He (or she?) will be too busy trying to work out how to turn the ignition on and open the bonnet. :D
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The first front brake pad connector in the circuit should be live so that if/when the brake pad wears out it will earth and light the bulb.

The MOT tester knows the car and had one for years so I don't need to tell him how to open the bonnet or not to jack on the sills.

quattro said:
quattro said:
The only brake pad switch (bullet connector) to be live with all of the pads disconnected would be the first one that the the circuit goes to, and I'm not quite sure which one it is.

Richard
Click to expand...

The first one is the front RH brake so if the connection to the reservoir is live, the wire then goes directly to the bullet connectors just inside the engine bay on the Right hand side.

I must admit that my handbrake warning light doesn't work since I got rid of these wires, so I am of to the garage to check it out :)

Richard
Click to expand...

That's what I thought too, but I don't get anything from those two connectors. I tried to separate the two wires from the fluid reservoir cap so as to determine which one is live and which goes tot he next part of the circuit but they're corroded together and I didn't want to brake the connectors just before the MOT.

Thanks for all your help with this, I'll report back on the MOT tomorrow lunchtime.
 
Just to round off this thread, the lack of a 'handbrake on' lamp wasn't mentioned in the MOT so EMF would have passed if I'd spotted that one of the top link bushes in the rear suspension had fallen to pieces - doh!
 
testrider said:
Just to round off this thread, the lack of a 'handbrake on' lamp wasn't mentioned in the MOT so EMF would have passed if I'd spotted that one of the top link bushes in the rear suspension had fallen to pieces - doh!
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Doh! indeed Paul. It's usually the obvious things you miss because you're so focused on the detail.

Easy fix though :D

Dave
 
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