Afternoon all,

Right, this one has been bugging me for absolutely ages now. Every now and then (it can be a period of a few miles or hundreds of miles), the nearside brake light fails (which I am notified by with the bulb symobol and an annoying bleep - the bulb does actually stop working too, I've checked that). I can't seem to work out what is causing it though as the offside bulb is always fine. I've removed the CD changer and checked the plugs in there - one has a bit of corrosion on it, but unplugging it while the brake lights are activated (typically they both work at the moment while I'm trying to diagnose the problem!) didn't make any difference, i.e., the plug seemed to have nothing to do with the brake lights. In fact, none of the three plugs under the CD changer seemed to have any effect on the brake lights!! There were some towing electrics fitted to this car, but I removed all the bits from that so I don't think that is the cause, either.

The last thing I've tried is wiggling every wire in sight inside the bodywork where all the wiring enters the boot, but yet still I can't get the thing to go off, but I bet it will go off again soon as soon as I start driving around anywhere.

Does anyone have any thoughts? If it was both brake lights, I'd assume the brake switch, but unless that has separate contacts for the nearside and offside brakes, I am stumped?!

On another note, does anyone know where the boot switch is? I noticed that while I was wiggling the wires, although I couldn't get the brake light to go off, the luggage compartment warning on the dashboard had a mind of it's own.

One last bit of info (if it's relevant) - there are two interior lights to the boot; the nearside one hasn't worked for ages (and was flickering for a while before it stopped working altogether).

Is there another plug somewhere that all this ties into that could be causing my problems? I can't see how a wire could have become broken, so I'm guessing it must be a plug or joint somewhere.

Cheers.

Just one more thing to check - tap the bulb while it is lit. I have had this problem with other cars due to 1) faulty bulb that was intermittent internally, 2) wearing away of the bottom connection of the bulb due to vibration over a high mileage.

Just one more thing to check - tap the bulb while it is lit. I have had this problem with other cars due to 1) faulty bulb that was intermittent internally, 2) wearing away of the bottom connection of the bulb due to vibration over a high mileage.

Thanks for the reply. I did try cleaning the bulb contacts as one the first things months and months ago, but it made no difference. Maybe I'll try changing the bulb and see how it goes, but I am still fairly convinced that the boot light failure on the same side is possibly linked in?

The earth seems solid too.

try using servisol silicone grease on the bulb base connections

Update: found the problem with the boot light; the towbar electrics fitted when the car was owned previously used a (crude) crimp in a silicone teat as a means of linking the interior light earths together. This had collected moisture and corroded away inside (I managed to pull one of the wires out of it by just handling it!). I've now soldered these up properly now and shrink-tubed them - so the boot lights are both working now.

As for the brake light . . . I'm a bit stumped. It wasn't working when I first went to the car earlier, then when I slapped the rear light cluster a few times, it started working again. I've checked for any more of the towbar electric bodges, but I can't find one that would influence the brake lights so I've drawn a blank. The only thing left now is where 'a' brake cable comes into the nearside rear wing, the towbar electrics had a scotchlock on the wire (which I subsequently removed). It's possible this has sheared the wires inside, so I'm going to strip it back and solder it up, but I doubt this is the problem as I can't see how slapping the rear light cluster would cause that connection, which is 2ft away, to make/break.

Sounds more like a bulb holder issue. Not too sure on the fitting but if it has a bit at the bottom that can be bent up try that

Sounds more like a bulb holder issue. Not too sure on the fitting but if it has a bit at the bottom that can be bent up try that

Again on a previous car, I had a similar fault where the springy piece that touches the bottom of the bulb was loose. The plastic holder had worn away allowing the the spring pressure to relax and the spring to move sideways. A touch of araldite fixed that.

I agree with the previous post that the light cluster/bulb holder is the place to look. Just remembered I had another fault where the connection between "brass" strips was made through a rivet that had corroded. Ah! the joys of French and British cars!

Cheers all. I had already taken some action this afternoon as a precaution along those lines; cleaned up the contacts, put a new bulb in (in the remote chance that the bulb itself is at fault, but it also provides some brand new contact surfaces too) and did check the spring tension on the contacts. The latter I had done before actually, so I am fairly sure that isn't the cause anyway.

Time will tell now - I went for a drive and didn't get the problem, but the intermittent nature means that I have no way of knowing if it's fixed or not. I guess I'll just have to see how things go!

Thanks again for the ideas/help.

Did you bend the spring up abit when you checked it?? May look ok but a tweek may fix it

Have you tried swapping the bulbs from side to side - that would help to indicate if it is a cluster/wiring or bulb issue.

Have you tried swapping the bulbs from side to side - that would help to indicate if it is a cluster/wiring or bulb issue.

+1

my sister had an indicator light that worked for a bit then stopped. We examined the bulb, looked ok, tested the bulb, worked ok, put it back in, did exactly the same. Then we tested again, but left on for 20s and it went out. Let it cool, worked again. Bulbs are so cheap, i reckon it's the first stop even if it looks ok

I have a MKII 2litre TDI DSG Octavia Estate with a similar problem to begin with reseating the bulb in it's holder cured it temporarily no sign of corrosion or poor contact has ever been found I then found a bulb that was blown glass blackened on my last look the filament was broken but no sign of having blown while hot I replaced it with a Halfords heavy duty bulb this has lasted just 4 weeks and is yet again requiring attention. I did find while checking that there are no double filament bulbs used and the brake light bulb glows at reduced intensity when the sidelights are on this I have only come across before when a warning has to be given exceedingly quick as it reduces the time prior to maximum intensity being reached, seems like a lot of complexity for very little gain to me.

Somewhere out there is an answer but like good politicians will I ever find one.

I did find while checking that there are no double filament bulbs used and the brake light bulb glows at reduced intensity when the sidelights are on this I have only come across before when a warning has to be given exceedingly quick as it reduces the time prior to maximum intensity being reached, seems like a lot of complexity for very little gain to me.

Are you saying the Octy mk2 uses a 21w bulb for a tail bulb and just applies less power to the bulb to make it the same brightness as a normal 5w tail? That sounds like the old sidelight thing my Nova used to do which was apply less power to headlight bulbs when the ignition was on rather than actually using the sidelight bulbs....

Octy 1 uses a 21/5 w combo to the best of my knowledge.

Are you saying the Octy mk2 uses a 21w bulb for a tail bulb and just applies less power to the bulb to make it the same brightness as a normal 5w tail? That sounds like the old sidelight thing my Nova used to do which was apply less power to headlight bulbs when the ignition was on rather than actually using the sidelight bulbs....

Octy 1 uses a 21/5 w combo to the best of my knowledge.

Yeah the Mk1 uses a twin-filament bulb. That's interesting about the dipped beam on low power; that would explain the way that some older cars have what appear to be extremely dim headlights on sometimes. Learn something new every day!

I wired up some towbar electrics on a new mini cooper s, got a bit stuck on the fact that the stop and tail light only had one lamp with only one filament!, after much headscratching and lots of testing it dawned on me that the newer mini's stop/tail light only has 6 volts applied to it for tail light and this voltage is increased to 12V when the brake pedal is pushed, why would they do that you ask? a single filament lamp is cheaper than a twin filament, only need to run one +ve wire to the lamp thus saving on wire, money saved means more profit, also means normal towbar electrics won't work properly! you need a special box o' tricks to keep the ecu happy.