Technical Brake Light Problem

[Fred Duck]

2007 plate Grande Punto 1200 8v. Yesterday, yellow warning triangle appeared and message 'Check Stop Lights'. Checked and near side stop light was out. Off side and central stop lights working as normal and both side lights on near side and indicators also working fine. Today, removed near side light unit and the stop light filament had blown. Replaced bulb with correct 21/5w bulb, back together and still no near side stop light. Removed light unit again. Checked and cleaned all contacts, still no stop light. Tested plug connector with Multimeter and 12v to side light terminal and to indicator terminal but only 5v to stop light terminal. That test carried out using same earth connection for the multimeter. Testing same terminal on off side, 12v. On the face of it, it seems that for whatever reason, signal to near side brake light is not sufficiant to light bulb. Can anyone point me in the direction of why that should be, please?

Thanks in advance,

FD

 

[DGPunto]

Have you tried swapping the bulbs nearside to offside in case it's your new bulb?

 

[oldmanhouse]

How is the condition of the wiring between boot and light? That is a common weak point worth checking out:

 

[Fred Duck]

Thanks for your replies. I've swapped the bulbs about and also tried a second new bulb but the problem remains. As far as I can see, the condition of the wiring is good with no deterioration evident. The basic problem seems to be that when I test the voltage available at the brake light terminal in the connector plug I get, at best, 5v. Same terminal on the other side, 12v. Connecting the near side light unit to the off side connector, it works fine showing that the issue is not related o the unit or the bulbs. Puzzling further is that all was fine on Monday until the stop light filament blew. I can't see how something as simple as a bulb blowing should cause the voltage at the terminal that supplies it to suddenly reduce.

FD

 

[Pugglt Auld Jock]

Thanks for your replies. I've swapped the bulbs about and also tried a second new bulb but the problem remains. As far as I can see, the condition of the wiring is good with no deterioration evident. The basic problem seems to be that when I test the voltage available at the brake light terminal in the connector plug I get, at best, 5v. Same terminal on the other side, 12v. Connecting the near side light unit to the off side connector, it works fine showing that the issue is not related o the unit or the bulbs. Puzzling further is that all was fine on Monday until the stop light filament blew. I can't see how something as simple as a bulb blowing should cause the voltage at the terminal that supplies it to suddenly reduce.

FD

It's got to be something to do with the wiring I would think? I'd start by checking at the contact in the light unit (with bulb removed) and then, if the result was unsatisfactory I'd pull the connector and check there - just as you say you have. So you got 5 volts? The problem may be further back but might be due to a poor connection between the wire and the connection in the plug. Get a sharp probe - I sharpen a bit of welding wire against my grinder until it's needle sharp and form the other end into a triangle so I can hold it easily. - Now connect a multi meter pos lead to this probe and the neg lead to a chassis ground and push the sharpened tip of the probe through the insulation of the relevant wire just "upstream" of the plug/connector until it makes contact with the wire inside. If you get 12 volts you'll know the problem is inside the plug but if you're still getting only 5 volts then probe further back up the wire and keep going until you hit 12 volts. Of course that sounds simple, in practice there are all sorts of problems with getting access to the wire, but you get the idea? Good luck, please let us know how you get on.

PS. wrap some self amalgamating tape round wherever you puncture the insulation or you might find the wire corrodes internally after a few years.

 

[Fred Duck]

Well, the problem appears to be solved. I know what I did but can't for the life of me figure out how it fixed it. After another afternoon of testing everything I could think of and getting nowhere, I removed the brake light fuse more in desperation than anything. The fuse was fine so I put it back in and hey presto, all brake lights working!! Given that the fuse serves all three brake lights, if it was faulty or a bad connection all three would fail, not just the one so I can't see how removing it and putting it back in would solve the problem but it did.

Thanks very much for your ideas and suggestions. They've been very much appreciated.

FD (I hates modern car electrics!!)

 

[Pugglt Auld Jock]

Well, the problem appears to be solved. I know what I did but can't for the life of me figure out how it fixed it. After another afternoon of testing everything I could think of and getting nowhere, I removed the brake light fuse more in desperation than anything. The fuse was fine so I put it back in and hey presto, all brake lights working!! Given that the fuse serves all three brake lights, if it was faulty or a bad connection all three would fail, not just the one so I can't see how removing it and putting it back in would solve the problem but it did.

Thanks very much for your ideas and suggestions. They've been very much appreciated.

FD (I hates modern car electrics!!)

As you say, that's not logical - but I'm glad for you that you've got the light back. I suspect though that you haven't truly "sorted" it and it's going to come back again - Hope I'm not right! If anything it would seem to suggest that there's a problem/poor connection or corrosion in the fuse box somewhere. There are others on here who have reported problems with corrosion in the fuse box - maybe someone who's experienced it could comment here?

 

[Fred Duck]

Yes, I agree. I fear I've only treated the symptom, not the disease. However, if/when it happens again at least I know now where to start looking.

Thanks again for all the help and advice.

FD

 

[Jan Buchik]

Definitely check your wiring. Had (and still have) the same issue, pulled off the right side brake light and found an ape with a soldering iron had ****ed the whole connector and loom with some house electrical connectors. Good way to check if its the loom that's screwed is by indicating on the side of the car who's break light is out, then braking. If the indicator skips a beat or speeds up for a second, its the loom