HELP: Why do my LED cab lights glow when off

[mikeonb4c]

Got a bit of a puzzle. My LED front cab light bulbs often continue to glow dimly (actually quite brightly, sometimes more than other times) even when cab lights are off, including if I turn the master OFF using the wheel on the cab light. There is clearly some leccy leaking in their direction, though it must be minimal as there is no sign of battery drain. Trouble is I'm no wiring expert and wouldn't begin to know what to suspect. I've opened and closed doors, pressed door switches, tapped fuseboxes, tapped the light unit, nothing seems to have any effect on it. The bulbs do have some aluminium foil around them to help lens the light into the cab, but they've been like that for years (and does aluminium conduct anyway?). I can't think of any wiring changes I've made in years. LEDs are funny bulbs - could they be kicking off over something you wouldn't even notice with a normal incandescent bulb?

The only other thought I've had is I have one or two episodes of the central locking not unlocking the other doors when I use the key in the drivers door. I posted a separate thread on that and the feeling was I might have a dodgy bit of wiring in drivers side door wiring loom (usual problem - wire fatigue where it constantly bends through opening and closing drivers door). Could this be connected (mind you I tapped that also and could see no effect on glowing of cab lights).

I'd welcome any thoughts. Is this the kind of thing I might expect an auto-electrician to be able to track down, if it is a wiring issue.

Thanks chums

[jimmo62]

I had the same problem. I think it is because there is sufficient reverse leakage in the diode pack (I3-06 on page 102 of the wiring manual) to allow the LEDS to glow.

[mikeonb4c]

I had the same problem. I think it is because there is sufficient reverse leakage in the diode pack (I3-06 on page 102 of the wiring manual) to allow the LEDS to glow.

Phew, I feel better already. You start to wonder if something dodgy is going on! Does yours still do it or did you dump the LEDs and go back to 'normal' bulbs (nicer light and brighter, from memory, and for the amount of use they get they are hardly a battery drain issue).

[jimmo62]

I went back to normal bulbs, I liked the idea of the lower drain but as you say it's not that bad with standard bulbs and I had plenty of other more pressing jobs to concentrate on!

[g8dhe]

There could be several possibilities as to the cause and the diodes above are just one of them.
With both the Spot and Door switches set to OFF then they should not be lighting, however any leakage across the switch or within the housing could allow them to glow, also they do reflect external light back very well which doesn't help either. You would need to use a meter to measure the current flowing to eliminate the most likely causes and track down the route for the current.

[mikeonb4c]

There could be several possibilities as to the cause and the diodes above are just one of them.
With both the Spot and Door switches set to OFF then they should not be lighting, however any leakage across the switch or within the housing could allow them to glow, also they do reflect external light back very well which doesn't help either. You would need to use a meter to measure the current flowing to eliminate the most likely causes and track down the route for the current.

Thanks Geoff. Although I have a multimeter I've only ever use it for voltage and resistance - I think a jumper has to be altered to measure current and woebetide me if I do it wrong? Also, I'm not great at understanding all but the most basic diagnostics. Do you think this kind of forensic work would be simple for an auto-electrician?

Definitely not external light as this is in the night time. Also, they can flicker between dim and less dim, so something's afoot I guess. Question is, if I'd not had LEDs in, would I ever have noticed it i.e. are old car auto-electrics an imperfect world?

[weebrian]

I've had the same problem with mains LEDs as well as low voltage types. I'm told that this is due to cheap Chinese circuitry and doesn't happen in more expensive units with proper quality monitoring. As regards the mains lights, I have even turned the main circuit breaker off and the leds still glow.

[jimmo62]

Just been out (in the rain!) to check with some LED bulbs. In my case, when the side sliding door is open, the cab lights come on dimly. With it shut, they are off. So I'm pretty confident that it is reverse leakage in the diodes - since that's the only way I can see current can flow/not flow depending on the side door

May be worth checking if you have the same situation, if so you might be able to fix by adding another (low leakage) diode in series with the existing diode pack

[wonkanoby]

contact cleaner in door contact push pins fixed mine

[mikeonb4c]

Fab advice all round - I'm greatly reassured that its not likely to be anything serious and is more a reflection of how little current LEDs need to activate. Will spray contact cleaner on switches, try removing that aluminium foil and - frankly - get back to the old fashioned bulbs that I love more anyway

Thanks everyone. Interesting thread too as it appears others have been suffering in silence until now, but this thread should prove useful to others in the future.

Geoff - still interested in your thoughts on diagnostics, though it may be that the posts of the others have pretty much solved the mystery

[g8dhe]

Diagnosing the actual cause is difficult to describe, but basically its a case of using the current range of the meter and connecting it in series with the LED's themselves, your probably talking of currents less than a 1milliamp. Then operating the various switches to see what happens to the current. It is probably worth giving the plastic cases and surfaces a clean as well as its not unknown for small leakage currents to exist across the surfaces. Another possible cause is radio frequency pickup on the wiring, this won't be measurable with the meter on DC Current and possibly not even on AC as the meters aren't normally designed to measure such high frequency currents/voltages.

[mikeonb4c]

Diagnosing the actual cause is difficult to describe, but basically its a case of using the current range of the meter and connecting it in series with the LED's themselves, your probably talking of currents less than a 1milliamp. Then operating the various switches to see what happens to the current. It is probably worth giving the plastic cases and surfaces a clean as well as its not unknown for small leakage currents to exist across the surfaces. Another possible cause is radio frequency pickup on the wiring, this won't be measurable with the meter on DC Current and possibly not even on AC as the meters aren't normally designed to measure such high frequency currents/voltages.

Thanks Geoff. What's weird is no flicking of switches, turning of starter motor, tapping the unit, hitting the car with a lump hammer etc. seems to affect the flickering at all. I think, rather as you and others are implying and rather as one does with PC software (i.e. don't waste time looking for what's wrong, just change something and see if it sorts it) I will do various things that would be worth doing anyway and see if any one of them stops the LEDs glimmering. If the glimmering persists, I'll move to the final solution: reinstallation of original filament bulbs, with the return of good old fashioned warmer light