10 replies to this topic

[pusb]

Wonder if anyone can offer any advice on getting my brake warning light working?

 

Currently as it is nothing happens if I press down on the button. No light at all. I have tested at the back of the switch and I am getting 12v to it.

 

However to confuse matters more, at my brake master cylinder I have no cables to attach to the reservoir cap. Mine was originally a drum brake set up that has been upgraded to servo so I think whoever done it has either cut the wires away or shoved them in behind the dash.

 

So my questions are:

 

When the button is pressed is that testing the bulb or the circuit? I know I have power to the switch, so presumably if pressing it is only testing the bulb, then my bulb must be blown?

 

What are the colours of the wires that should be attached to the master cylinder? Where abouts do they come from?

 

If anyone can help I would be most grateful!

[Scorp]

Pressing the button tests the bulb

 

Even if it does all work the reservoir cap is probably knackered mine was anyway 

[pusb]

So likely my bulb to have gone then?

 

My reservoir cap probably is as well! But I would like to at least try and get it working.

[pusb]

Well I'm not sure now if I've made progress or not.

 

After much snooping round the back of the engine and speedo I managed to find the cable that runs from the test switch to the brake cylinder:

 

 brake switch cable.jpg   16.17K   16 downloads

 

I then thought if I short these two cables (to simulate a loss of fluid) then the switch should light up. So I gave it a go:

 

 switch shorting.jpg   20.65K   13 downloads

 

I looked back at the light, and nothing. It still wasn't lit. However when I pushed the switch it did light:

 

 switch light.jpg   22.71K   8 downloads

 

So now I'm really confused. What else should be in the circuit for it to light up on its own? Should there be an earth point at the brake cylinder?

 

At least I know the bulb is working!

Edited by pusb, 08 May 2014 - 07:12 PM.

[maccers]

As far as I know from my own setup, it looks like your cap is at fault. As you have made a loop back with the wire, and when you press the switch it lights, which is what should happen when the plug is connected to the cap. I took my old cap apart to clean but it was badly furred up, so I bought a new one, and it worked as it should do. Get a new cap or try and take it apart to clean. The switch and wiring side looks good as you have proved with your loopback cable.

[Steve8274]

Surely the switch light should have lit up when he made the loop. It only lit when he pressed button.

[pusb]

Surely the switch light should have lit up when he made the loop. It only lit when he pressed button.

 

That's what I'm thinking. My thought was the loop should have simulated a brake problem.

[KernowCooper]

Here is the brake fluid warning light circuit

 

62 is the switch

67 is the warning light in the cap

 

When you press the switch which is shown by the 2 arrows you just give the bulb a earth via the loop of the Black/white on the Black (BK) wire the feed in is the Purple (PU) so the light comes on.

 

Now look at the Black/white (BK/w) circuit this has a direct earth through the cap once the fluid  level drop and the cap contact is made.

 

Its designed and wired that way so you have a test of the circuit and a warning light for low fluid

 

See that the wire from the cap is actually getting a earth otherwise the low fluid light won't come on, the diagram gives you  the full circuit so you can pinpoint where the fault is, a continuity test from switch Black/white and the outside Black/white can be carried out to ensure the cables not broken

Attached Files

•  Brake Fliud Warning Circuit.png   37.53K   48 downloads

[pusb]

Thanks kernowcooper, that's exactly what I'm looking for!

There is no earth connection at the cap so that will be where my problem is.

Thanks for you help.

[Dan]

Sounds like your car has been converted from a PDWA warning system, or rather it should have been and hasn't. You will need to make some minor changes that were listed in the BL service bulletin published when PDWA systems became obsolete. I'll see if I can find the document when I get home but you should find it online. It's on the forum somewhere and in Haynes.

[pusb]

Thanks dan