Technical Boot light troubleshooting (getting voltage but no light)

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Technical Boot light troubleshooting (getting voltage but no light)

sito

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Hello everyone,
I'm trying to solve an issue I'm having with the boot light on my 500 (pop, 1.2, 2009).
After consulting multiple threads here and elsewhere, I've decided to add an aftermarket light since in my case, there was a loom, but no factory-installed bulb/bulb enclosure. When I tested the connection using a multimeter, I was getting around 12.35 volts with the boot open which then dropped to 0 volts after several minutes, which looked good.

I've managed to successfully install a standard 12 volt LED strip (about 1 metre long) to the existing wire (the added connector is not shown on any of the photos).
When connected to the factory wires and measured, the strip is getting the proper 12 volts it needs (when the boot is open) as shown on the photo - I measured this on multiple points on the strip (both near the connector and towards the end), but it does not light up at all for some reason.

Note that the strip and its wiring/connection is fully functional, as shown on the next photo (when attached to a 12 volt li-ion battery from a cordless screwdriver). I also a 'regular' non-lithium 9 volt and it lit up dimly.
I've tried closing and opening the boot several times and actually locking and unlocking the car to no avail.

I've read that there is no canbus connection for the bootlight on the 500, so I am not sure what am I doing wrong. It does not seem to be the issue of voltage, polarity, poor connection... could this have something to do with the current draw? I don't have a W5W or a similar bulb handy so I cannot really test if a "regular" non-LED bulb would work.

Thanks for any advice.
 

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I'd agree that polarity is likely the culprit. I installed an LED light in my boot a couple of years ago with a wired dummy plug inserted into the light socket and it worked either way because the light had an inbuilt rectification chip. There were no problems at all.
 
Thank you both, mystery solved - it was the polarity and I guess a case of Friday evening's overwork :rolleyes:

I intuitively connected the factory black wire (with a barely visible red strip) to the connector's negative side and the white/yellow wire to the positive one and just quickly tested if I was getting voltage - entirely missed that the voltmeter is showing negative 12 volts.

Just switched it (white/yellow connected to LED's negative, black/red to LED's positive) and it lit up.

Looks a lot better than having no light at all. I'm attaching some photos for future readers who might have the same problem :)

One thing to note (not sure if anyone else is/was experiencing this) - when the boot is closed, the strip gets 0 volts. Open, it gets around 12.3 volts, as I've mentioned. But after leaving the boot open for around 10+ minutes, the voltage drops to around 0.3-0.5 volts (not 0) which actually causes the LED strip to flicker. It is barely visible though and does not happen with the boot closed so I'm not worried about draining the battery. Just found it interesting.
 

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Glad to hear it's sorted. I expect the drop in voltage is like the interior light being switched off after about 15 minutes if you leave it on but I didn't know the boot light would do it too. Curious that it doesn't cut power completely. I'll try leaving my boot open to see what mine does.
 
Thank you both, mystery solved - it was the polarity and I guess a case of Friday evening's overwork :rolleyes:

I intuitively connected the factory black wire (with a barely visible red strip) to the connector's negative side and the white/yellow wire to the positive one and just quickly tested if I was getting voltage - entirely missed that the voltmeter is showing negative 12 volts.

Just switched it (white/yellow connected to LED's negative, black/red to LED's positive) and it lit up.

Looks a lot better than having no light at all. I'm attaching some photos for future readers who might have the same problem :)

One thing to note (not sure if anyone else is/was experiencing this) - when the boot is closed, the strip gets 0 volts. Open, it gets around 12.3 volts, as I've mentioned. But after leaving the boot open for around 10+ minutes, the voltage drops to around 0.3-0.5 volts (not 0) which actually causes the LED strip to flicker. It is barely visible though and does not happen with the boot closed so I'm not worried about draining the battery. Just found it interesting.
That looks amazing! And I bet it’s a lot brighter where did you find the led strip?
 
They are easy to find on eBay and Amazon just look for 12v led strip lights
I've got some sat around the house some place left over from when fitted s light just like this in my 500
Chris going to wire in my strip in boot but not sure of connections strip has a red and a black wire but boot light has red and a white wire am I missing something obvious ?
 
Someone in a different forum made a detachable contact on the hatchback with aluminium self adhesive on the two pins that the shelf clips on to and corresponding contacts on the shelf left and right.
I have it easier in the C as nothing can/ needs to be detached...

I added diodes (2 I think) in series with the (2nd) led strip as the voltage tends to rise to 14.4 Volts when the engine is running which kills led strips that don't have protection (which is the case for most cheap strips). My first strip had a few bad elements after a year.
The 2nd one is fine after a similar time.
 
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