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Discussion Starter #1
Hi all,

Boot light didn’t work on my recently acquired 2014 ceed. so, I ordered replacement and fitted - it still doesn’t work. I took the bulb out and tested it with a 12 V battery and it works fine. After a closer look, I noticed what looks like a small Diode on the Bulb holder. Could this be the issue.?
Do I need to replace the diode, or the whole bulb holder?

Here is a picture of the bulb holder.
 

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I would check you actually have 12v at the light, otherwise it'll never work.

Check the fuse supply and that the switch is working.
 

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Discussion Starter #3
Ok - i’ll do that too. However when the bulb holder is provided with 12v power from an external source it doesn’t work - so I need to fix that too.
 

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The diode will make the lamp polarity sensitive, so it will only light if connected the correct way round. You can test the diode if you have a multimeter - it will have a much lower resistance in one direction than the other.


If the diode is open circuit in both directions you can get a replacement - remove it and there sill be a part number 1N4004 or similar and these are available from Maplins or Radio spares for pennies. Make sure that you put the replacement in the same way round (note which end the stripe is)
 

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Discussion Starter #5
Thanks turnup. I’m Not familiar with modes of failure for rectifiers - it is closed circuit in both directions...

I’ve ordered a replacement diode and will give that a go.
 

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Erm.......closed circuit both ways would not fail the boot light. Closed both ways is an unusual failure mode (very rare but not unheard of) Open both ways is much more usual and this would fail your boot light.


Not entirely clear in the picture but does the light have three connections and it's own switch?
 

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The diode will make the lamp polarity sensitive, so it will only light if connected the correct way round. You can test the diode if you have a multimeter - it will have a much lower resistance in one direction than the other.


If the diode is open circuit in both directions you can get a replacement - remove it and there sill be a part number 1N4004 or similar and these are available from Maplins or Radio spares for pennies. Make sure that you put the replacement in the same way round (note which end the stripe is)
As far as I know Maplins is ancient history!! RS Components will be expensive so I'd recommend searching fleaBay for a 1N4004, there are plenty of sellers but choose a UK supplier else it will take weeks to arrive. Most UK sellers of electronic components seem to deliver withing two days.

Looking at the photo it's a bit of a mystery what the diode is for - or even how it's connected. Usually a diode, in a DC circuit, is to force a particular polarity and/or stop volts feeding back into other circuits, say if there were two switch feeds but the picture only shows two connections. I assume one is +ve feed and the other -ve ground, unless they are both +ve feeds and the lamp module gets a ground connection when it's pushed into the car body which would be a little unreliable but would explain why it does not work when outside of the body.

It would be interesting to know what the diode is for - anyone with a wiring diagram?

Final thought are you replacing with a filament lamp or LED? If an LED it will only work in one particular direction so turn the bulb round.
 

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As far as I know Maplins is ancient history!! RS Components will be expensive so I'd recommend searching fleaBay for a 1N4004, there are plenty of sellers but choose a UK supplier else it will take weeks to arrive. Most UK sellers of electronic components seem to deliver withing two days.

Looking at the photo it's a bit of a mystery what the diode is for - or even how it's connected. Usually a diode, in a DC circuit, is to force a particular polarity and/or stop volts feeding back into other circuits, say if there were two switch feeds but the picture only shows two connections. I assume one is +ve feed and the other -ve ground, unless they are both +ve feeds and the lamp module gets a ground connection when it's pushed into the car body which would be a little unreliable but would explain why it does not work when outside of the body.

It would be interesting to know what the diode is for - anyone with a wiring diagram?

Final thought are you replacing with a filament lamp or LED? If an LED it will only work in one particular direction so turn the bulb round.

Maplins are back on-line only :) but it seems that they no longer do components :-(
 

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As far as I know Maplins is ancient history!! RS Components will be expensive so I'd recommend searching fleaBay for a 1N4004, there are plenty of sellers but choose a UK supplier else it will take weeks to arrive. Most UK sellers of electronic components seem to deliver withing two days.

Looking at the photo it's a bit of a mystery what the diode is for - or even how it's connected. Usually a diode, in a DC circuit, is to force a particular polarity and/or stop volts feeding back into other circuits, say if there were two switch feeds but the picture only shows two connections. I assume one is +ve feed and the other -ve ground, unless they are both +ve feeds and the lamp module gets a ground connection when it's pushed into the car body which would be a little unreliable but would explain why it does not work when outside of the body.

It would be interesting to know what the diode is for - anyone with a wiring diagram?

Final thought are you replacing with a filament lamp or LED? If an LED it will only work in one particular direction so turn the bulb round.

That must be what it's about. Looking carefully at the pic there just might be a switch in the lamp housing so the light can be on with the switch or on with the interior lights (might even be an off position). But as you point out that would require three connections. Anyway bridging the diode will prove if it is open. There will be some unexpected interaction between the interior lights and the boot light but it will do no harm,.
 

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Discussion Starter #12
Thanks all. Two terminals and No switch built in to the housing as far as I can tell. I am replacing with LED, but i’s one of those ones with rectifiers and crossed over wiring built in so it will work in either direction. The old incandescent bulb still works, but doesn’t work in the housing with either polarity connected to the housing terminals.
I’ve ordered some of the diodes IN4004 from a uk seller. Should arrive by week end.
 

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Thanks all. Two terminals and No switch built in to the housing as far as I can tell. I am replacing with LED, but i’s one of those ones with rectifiers and crossed over wiring built in so it will work in either direction. The old incandescent bulb still works, but doesn’t work in the housing with either polarity connected to the housing terminals.
I’ve ordered some of the diodes IN4004 from a uk seller. Should arrive by week end.
Putting the housing to one side can you use a cheapo multimeter (if you don't have one a cheapo one will be a valuable addition to your tool box) to check that there is 12 volts on the connectors when the lamp should be on, you may have to locate the switch which controls the boot light to make sure that is working correctly. You could use the old bulb and some twisted wire if you are confident about that. Check between each of the wires in the connector and to car chassis (-ve).

If you have no luck can you take some more photos from different angles so we can try to understand the fitting and how it should work?

There are some pics of a similar lamp assembly in https://www.kiaownersclub.co.uk/forum/35-rio-2011-2017/19607-ki-rio-interior-light-replacement-guide-led.html which shows a boot lamp housing like yours but without the diode https://www.kiaownersclub.co.uk/d2/uploads/13162/15.jpg This tends to confirm that the two connections are just +ve & -ve and the diode is extra in your case.

Another thing is check for a secondary fuse location, a friend had a car which had a rear fuse box as well as the front one and had a similar problem tracing an apparently 'non working' lamp.
 

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Thanks all. Two terminals and No switch built in to the housing as far as I can tell. I am replacing with LED, but i’s one of those ones with rectifiers and crossed over wiring built in so it will work in either direction. The old incandescent bulb still works, but doesn’t work in the housing with either polarity connected to the housing terminals.
I’ve ordered some of the diodes IN4004 from a uk seller. Should arrive by week end.
The on /off switch is built into the tailgate latch.

The diode is easily tested with a multimeter. Should be open circuit in one direction, and give a measured resistance the other way.

But surely you should be checking for 12v at the light when the boot is open first?

Isn't it more likely that its a power supply issue than failure of a static component?
 

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The on /off switch is built into the tailgate latch.

The diode is easily tested with a multimeter. Should be open circuit in one direction, and give a measured resistance the other way.

But surely you should be checking for 12v at the light when the boot is open first?

Isn't it more likely that its a power supply issue than failure of a static component?

The OP has already stated that the diode is open circuit both ways so it is definitely faulty.


If there are only two connections then the diode would seem to be superfluous - perhaps it is a standard fitting used also in other installations? Anyway you can safely bridge the diode.
 

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Had exactly the same issue with my 2014 Pro-Ceed, thought it was the bulb at first, replaced it and still did not work, a new bulb unit was fitted under warranty by Kia.
 
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