Led bulbs t5 3w3 2smd polarity

Hello. Do you know if those led bulbs has a polarity? They are t5 w3w. I installed them in my third stop light on my car and they burned the fuse. Is it possible they’re too big for the installation? Change the position of some of them but still doesn’t ligth. Test them with multimeter and it beeping but again they doesn’t light. Two of them were not installed, just tested by multimeter and they give the same result as on the photo below and doesn’t light too.


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Hi Ron
Yes all LEDs are polarity conscious unless you feed them with a diode bridge but that only happens in special circumstances.
They should be tested (and polarity established) using the diode test which is 2 positions around from where you show in the pic. With this test positive voltage is on the positive meter lead and when forward connected the LED should glow dimly and the meter might not show the forward voltage drop as the whole thing is 12V but I established polarity with this method OK.

Why they failed using the continuity test I have no idea.
Cheers Bob

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Since i don’t have other options for test, can I mark them as defective and return? Other users recommended me those bulbs, which are slighty different and close to the old style bulbs

These bulbs are not polarized, and are marked as AC/DC, so it doesn’t matter which way around they are installed. The only requirement is that they are 12V, so there is no reason that they wouldn’t work just fine as a replacement for any similar 12V bulb in the vehicle. One reason that they might blow a fuse is if they don’t quite match the socket, especially if you inserted them when the power is applied - I have experienced similar items that were manufactured with enough difference from the standard to short the terminals as they were inserted or removed. Or, they just might not match your sockets - the second example you give seems to be for a very different socket. Given that they have a rectifier and circuitry to handle 12V with a LED, I don’t think you will get sensible values testing with a multimeter. The way to test them would be with a 12V supply connected direct to the contacts.

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They are maybe 1mm larger than old ones but fit tightly. I’m thinking their material at the bottom is something different from glass or plastic but looks like wood. The other type i posted later was found in a video, where the guy just installed them. They will fit, the picture is zoomed probably. But don’t know if will light or not. Chinese bulbs are lottery

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The material used for the separator in that first one is probably PCB, either fibreglass or a type of pasteboard. 1mm size difference is a lot, and it is possible that the connectors in the socket were pushed against each other or against the shroud. Or the problem is in the arrangement of the connecting tabs - if they are too large or misaligned then they will bridge across the terminals in the socket and blow the fuse. It would be unusual for a faulty globe to fail with a short that blows the fuse - much more likely that it just refuses to work.

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You’re maybe true. I found way to test them - with larger battery and piece of wire. All of them light up. So they are not defective. Just not suitable for the place where I installed them

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Hi Jeff

Well spotted. I completely missed that until I had a closer look. I have new spectacles too. Getting slack in old age.

That being the case they must have a built in bridge and you certainly can insert them either way.

I did spot that. The replacements MUST have the same socket as the old lamps.

Thoroughly agree with that. The extra 2 diode drop (1.2 - 1.4V) in a bridge would be too much for the DMM diode test
Cheers Bob

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Ok. So I may try with the same style led bulbs

Hi @Ron280737

From personal experience with messing with T5 LEDs in my car I found that they had a propensity to burn out quite quickly, what I found was the issue in my case was that while a car generally will run on 12V, it could be as high as 14.5V with the alternator running, the second type of bulb that you sent through are just a 5mm LED with a resistor housed in the plastic sheathing and the legs of the LED and the resistor bent up. You may have luck with soldering in a slightly higher value resistor.

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Dan, are you claim that those red bulbs are also not suitable for my car? Today checked carefully what happened with the brake light and found only 2 of 8 bulbs light up(my old bulbs not leds). Seems terminals are shorted. Don’t think will be able to fix, so will order anoher brake light

Hi @Ron280737

It will really depend on your car and the LEDs you have, mostly just sharing my experience with trying to use similar ones and the issues that I ran into.

Hi Ron
One of the main things you need to watch is make sure the replacement lamps have the same connecting arrangement as the old ones. So far there have been pics of 2 arrangements (I forget what the arrangement is called now) and you have not indicated which one is the correct one so whether the bulbs as shown are or are not suitable for your car cannot be stated. You have the bulbs in front of you, we don’t so you are at a decided advantage here. If it were my car the one you show at the top in the callipers would be correct.

Are you measuring the “shorted” terminals with or without any other bulbs present. Those would all be connected in parallel and if you measure with any others fitted the resistance measured would be pretty low. Assuming the original incandescent ones here. The cold resistance of an incandescent lamp is quite low and does not reach operating resistance until it gets hot, that is illuminated.
Cheers Bob
PS. If you purchase a new lamp it will probably be fitted with the original (incandescent??) type of bulb.

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Already replaced brake light and fitted new halogen bulbs. Two of them again defective, few other with bended springs, which I corrected. Quality of new parts is terrible. On my old brake light, i see that metal part, which contact with the bulb, is coroded. Maybe that’s why fails

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