tim hunt Posted June 23, 2023 Report Share Posted June 23, 2023 (edited) For weeks my LED parking light bulbs perform normally then one day I notice that the RH is much dimmer than the LH (see pics). If I swap the bulbs the RH is still much dimmer so the problem is clearly not with a particular bulb. Thinking I might have poor connections I have tried cleaning up the bulb holder with emery paper to no avail. Doe anyone have any 'bright' ideas, I am tearing my hair out. I apologise for antipodean image, always seems to happen with iPhone for some reason Tim Edited June 23, 2023 by tim hunt Quote Link to post Share on other sites
RobH Posted June 23, 2023 Report Share Posted June 23, 2023 (edited) Just a bad connection. The wires for both lights go back to a double bullet connector so if the connection at the bulb-holder is good the problem might be there. Since one of them is working it can't be further back than that. Is the earth on the bulb-holder ok? Edited June 23, 2023 by RobH Quote Link to post Share on other sites
Andy Moltu Posted June 23, 2023 Report Share Posted June 23, 2023 Swap the bulbs over and confirm if it is the bulb or the holder/wiring. If the bulb is the cause you could waste a lot of time. (Some, but not all LEDs will give out the same light level irrespective of voltage supply until it is so low they don't light at all. That's why many require dimmers that effectively pulse rather than Lowe the voltage.) Quote Link to post Share on other sites
RobH Posted June 23, 2023 Report Share Posted June 23, 2023 18 minutes ago, Andy Moltu said: Swap the bulbs over and confirm if it is the bulb or the holder/wiring. Andy - if you read the whole post you will see he has already done that. Quote Link to post Share on other sites
tim hunt Posted June 24, 2023 Author Report Share Posted June 24, 2023 15 hours ago, Andy Moltu said: Swap the bulbs over and confirm if it is the bulb or the holder/wiring. If the bulb is the cause you could waste a lot of time. (Some, but not all LEDs will give out the same light level irrespective of voltage supply until it is so low they don't light at all. That's why many require dimmers that effectively pulse rather than Lowe the voltage.) As Rob says Andy. I have just checked with a multi-meter and I find 12.55V across the battery terminals and an identical reading of 12.03V on BOTH sides if I check between the live feed and the side of each bulb holder. It doesn't look as though I have a high resistance somewhere by virtue of a bad connection. The plot thickens Quote Link to post Share on other sites
RobH Posted June 24, 2023 Report Share Posted June 24, 2023 6 minutes ago, tim hunt said: 12.03V on BOTH sides if I check between the live feed and the side of each bulb holder. It doesn't look as though I have a high resistance somewhere by virtue of a bad connection. You can't tell by using a digital meter. It draws so little current that even a very bad connection will not show up. Try using an incandescent bulb with wires attached. Also make sure the earth is good at the bulbholder - the supply may be OK but the current needs to flow to earth. Quote Link to post Share on other sites
stillp Posted June 24, 2023 Report Share Posted June 24, 2023 2 hours ago, tim hunt said: As Rob says Andy. I have just checked with a multi-meter and I find 12.55V across the battery terminals and an identical reading of 12.03V on BOTH sides if I check between the live feed and the side of each bulb holder. It doesn't look as though I have a high resistance somewhere by virtue of a bad connection. The plot thickens You've got a bad connection somewhere if you're dropping 0.52V between the battery and the sidelights. Pete Quote Link to post Share on other sites
tim hunt Posted June 25, 2023 Author Report Share Posted June 25, 2023 23 hours ago, RobH said: You can't tell by using a digital meter. It draws so little current that even a very bad connection will not show up. Try using an incandescent bulb with wires attached. Also make sure the earth is good at the bulbholder - the supply may be OK but the current needs to flow to earth. A good idea Rob. I thought I would simply fit two original type Lucas BA9S 4 watt incandescent filament bulbs - guess what, to the eye they looked equally bright. I then refitted the LED bulbs with the same result, as can be seen from the attached picture - they are now very similar in appearance! I do nit understand it, I have done nothing to the circuitry to make this difference, I guess it is just 'one of those things' - don't you just love these cars! However, I take Pete's point, I did think half a Volt was quite a loss over a relatively short wire run so will be looking carefully at all connections. The issue must be somewhere before the feeds to the two lights diverge, since voltage reading was the same at both. Tim Quote Link to post Share on other sites
RobH Posted June 25, 2023 Report Share Posted June 25, 2023 I think your incandescent lamp has pulled enough current to clean up a poor connection. The LED lamps don't take much current (though a whole lot more than the meter) and its possible an oxide film had built up somewhere. Either the higher current for the 'real' bulbs has burned through that or the physical act of inserting them has cut through it. Quote Link to post Share on other sites
tthomson Posted July 3, 2023 Report Share Posted July 3, 2023 On 6/25/2023 at 12:41 PM, RobH said: I think your incandescent lamp has pulled enough current to clean up a poor connection. The LED lamps don't take much current (though a whole lot more than the meter) and its possible an oxide film had built up somewhere. Either the higher current for the 'real' bulbs has burned through that or the physical act of inserting them has cut through it. That is precisely what I thought. It only takes a very small amount of corrosion on the bulb holder to prevent an LED form working optimally, whereas the current draw from an Incandescent lamp cuts through the corrosion to re-establish a decent current path that can then be used by the LED. Quote Link to post Share on other sites
Steve-B Posted July 4, 2023 Report Share Posted July 4, 2023 I learned from my dad that anytime you have such difference to have a pencil rubber with a bit of 60 grit glued on it. Take the bulb out, scratch around with the sandpaper, use a cotton bud with wipe out any excess and then retry. Has always worked for me over the last 40 years on numerous cars. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted July 4, 2023 Report Share Posted July 4, 2023 (edited) 1 hour ago, Steve-B said: I learned from my dad that anytime you have such difference to have a pencil rubber with a bit of 60 grit glued on it. Take the bulb out, scratch around with the sandpaper, use a cotton bud with wipe out any excess and then retry. Has always worked for me over the last 40 years on numerous cars. I’ve used a fibre glass scratch pencil for many years in the same way as you describe. Notably for cleaning metal surfaces prior to soldering when building etch brass models. https://www.halfords.com/motoring/paints-and-body-repair/fillers-and-preparation/abrasive-pencil-4mm-232470.html Edited July 4, 2023 by BlueTR3A-5EKT Quote Link to post Share on other sites
Lebro Posted July 4, 2023 Report Share Posted July 4, 2023 Yep, I use the same, very useful tool. Bob Quote Link to post Share on other sites
Trev Good Posted July 14, 2023 Report Share Posted July 14, 2023 (edited) Just caught up with this thread and I have noticed a really weird phenomenon with LEDs that someone much more experienced with them may confirm and explain! I have a bunch of dashboard LEDs as I was going to use them on another classic. But! A third worked on positive earth or negative earth, a third only worked on negative earth and a third were dim on positive earth! Could this be your reason? Edited July 14, 2023 by Trev Good Quote Link to post Share on other sites
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