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Technical Brake light fail indication but all stop lights working

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Technical Brake light fail indication but all stop lights working

Peat

Peat

Grumpy Old Manx Git
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Brake light fail indication but all stop lights working. 3 dr JTD 115 2002

I had this problem at the beginning of the year and cured it (or so I thought) by adjusting the switch plunger as per Deckchair's excellent guide.

The brake lights have worked fine all summer but with the onset of the damp weather the fault has reappeared so I treated the car to a new brake switch because I have just retro fitted a cruise control which I felt would have no problems with a good working brake switch.

Sad to say, no difference, the brake lights (lo & Hi level) work fine but the "Brake warning fail" & triangle sign are still there.

I had thought the dampness was causing intermittancy in the switch because it worked after a reasonable time driving with the heater on but this is obviously not the case.

Any ideas would be welcome.
 
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Problem is generally caused by poor contacts at the bulb. Clean the contacts in the bulb sockets and the contact points on the actual bulbs. The high level brake light uses LEDs and doesn't usually cause the bulb failure warning to come on.
 

Thanks for the swift reply Davren.

I have cleaned the nearside contacts with no luck. Tomorrow I will check the offside. There was no indication on the dash with regard to which side was at fault. Is this indicator only on later models?
 
Hi.
I had this problem I just put two new bulbs in even though they both worked, problem solved £1.20
I think the indicator is just a little arrow beside the words brake light failure, easy to miss.
 

Just spent three hours removing the rear light clusters, cleaning ALL the contacts and spraying with contact cleaner, changed bulbs, cleaned those earth contacts on rear of inner wing, even removed the brake switch again & sprayed with cleaner and re-adjusted and still I get the warning triangle + "Brke. light fail" message.
Where do I look now?
Would it be a poor contact on the Body Computer? If so, where is it located?

 
I have changed the rear bulbs several times (have a handful of cheap bulbs), and I actually get the error message several weeks before they really blow. It's like the voltage throught them differs some time before the burn off the glowthread. I have this fault right now, and got my wife to push the brake pedal for me. And the right one is actually shining brighter than the left one - which I guarantee will blow in a week or two (the right one that is).

Try changing the bulb.
 
Yellow Peril said:
'Burning off the glowthread' - I like that phrase Mort. Haven't a clue what it means, but it sounds good!:)
Click to expand...

:D:D:D

Haha, it was directly translated from Norwegian. Please help...

Inside the bulbs there are some metal wires (wolfram or tungsten) that actually glow when they get current. So the bulb looks bright. :D So... thin metal wire = thread, in this problematic example.

After a while these "glowthread" always burns off. Here, classic bulbs are called "glowbulbs", and inside them there is a "glowthread" that "burns" while it is lit.

In the brake light bulb of the Stilo, there are two "glowthreads", one for regular rear stop light, and one for the brake - same bulb. Ooooh.
 
Morty Mort said:
I have changed the rear bulbs several times (have a handful of cheap bulbs), and I actually get the error message several weeks before they really blow. It's like the voltage throught them differs some time before the burn off the glowthread. I have this fault right now, and got my wife to push the brake pedal for me. And the right one is actually shining brighter than the left one - which I guarantee will blow in a week or two (the right one that is).

Try changing the bulb.
Click to expand...

So Morty, are you saying that I should keep trying different bulbs until the fault clears?

How does that account for the fault disappearing throughout the warm summer months and after driving for roughly ten miles?

It would seem to me to be caused by humidity somewhere. The question is, where?

 
Probably a bad earth between the rear light cluster and the car body. Put a voltmeter between the cluster earth connection and a good clean shiny part of body metal like the boot lock, then put your indicators and sidelights on, you may even see the sidelights dimming in time with the indicators. If there's any significant voltage (when it should be very near zero of course) then there's your problem, need to find the body earth connection there and clean it up
 

Again thank you for your help.

I don't suppose you would know the locations of earth points C30 & C31?
 
Have to go hunting:)
earth point C30 C31.JPG
just follow the black wires
But if it's displaying near 0v between the cluster and a good earth then you can forget looking for them
 
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Found them but at the rear of the arch not the front. They're 12mm studs welded to the arch. Cleaned them and no difference. Will check for high resistance/voltage drop tomorrow all being well. Have you any idea what the small boxes are that the earth leads run through.
 
Will check for high resistance/voltage drop tomorrow all being well.
Now you should have done that first, find the fault and then fix the fault:)

Have you any idea what the small boxes are that the earth leads run through.
No. I don't know what you mean there

NB when you say you've "cleaned the contacts" do you mean the bulb contacts or the light cluster electrical connector contacts? The electrical contacts are prone to tarnishing so clean up with a pencil eraser and then some electrical contact cleaner. Then see if you can carefully bend the connector spring contacts to make stronger contact

The connector at the BC, should you need it, is connector E pins 22 and 32 which are feed for each side of brake lights. You could check resistance from those pins to earth to see what the BC is seeing
 
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The small black box that is connected to the chassis (C30,C32) is in fact a multiway connector even though there is only one earthing wire passing though it. Took it apart and sprayed with contact cleaner and have also once again cleaned and ensured good contact on the bulb spring connectors.

The measured resistance from the white multiway you have shown to the C30/31 earth studs is 0.1ohm, this is identical to a measurement between two scratch marks on opposite sides of the boot floor, so assume that is OK.

Although it is a nice sunny day here my back is complaining so I will return to it another day and try your suggestion, on the sprung contacts of the white connector, which have only just seen.

As I sit here I have noticed a double sided nail file board and wonder should I use that to roughen the contacts surface?

Nearly forgot, can you tell me where the Body Computer is located? Would I be correct in thinking it is in the central console?
 
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