Resistor Needed for LED Back-up Retrofit?

I bought a pair of LED bulbs to replace the OEM incandescent back-up bulbs in my 2013 Fiat 500. When I install both LED bulbs, neither one lights up. If I install one LED and one of the OEM incandescents, both bulbs light up. Because the LED bulb is a good bit brighter than the OEM incandescent, I would sure like to have both of them working. Why no lights with both LEDs installed? Is it possible that there is some sort of circuit in there that needs to see X-amount of resistance - or the car thinks the OEM bulbs are burnt out? Maybe a resistor would be a good work-around? If so, how do I size the resistor?

Thanks!!

PianoV said:

I bought a pair of LED bulbs to replace the OEM incandescent back-up bulbs in my 2013 Fiat 500.

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Unless you got the Philips Xtreme Vision LED with P/N 12841B2, you've no hope of getting an LED drop-in to work properly-- both in terms of them both lighting up, but producing a compliant reverse lamp pattern.

The vast majority of LED 'drop-ins' are unsafe, ineffective, and illegal.

Alaric is right; almost all the "LED bulbs" on the market are unsafe and illegal. Which ones (exactly) did you buy?

Am I correct that the Philips LED is $20+ for just one piece? $40+ for a pair that Alaric mentioned?

That would be an expensive reverse light if it is. Mines is GE Nighthawk which is a little bit brighter than the stock.

The correct Philips LED bulb for the '13 Fiat 500 is not the 12841B2, it is the 12832X1. I have this exact bulb in my car and my truck, and I like them a lot. Yes, they cost about $20 apiece. That is what it costs to have a real, working bulb made by a legitimate company instead of no-name junk that doesn't work. The Philips bulb also lasts long enough that you'll likely never have to replace them again, and they are quite a lot easier to live with when backing up.

don.gwapo said:

Am I correct that the Philips LED is $20+ for just one piece? $40+ for a pair that Alaric mentioned?

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Amazon is sold out of them, but they're listed at $23.12 each.

That would be an expensive reverse light if it is.

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Yep! But hey, LED!

Alaric Darconville said:

Amazon is sold out of them

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Doesn't look like it. Click the link I provided (to the correct bulb for the Fiat).

-Virgil- said:

Doesn't look like it. Click the link I provided (to the correct bulb for the Fiat).

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I went by "921", which Philips had as 12841B2 at http://philipsxtremevisionled.com/, but I didn't click on the X-tremeVision LED Exterior Lights tab. That tab doesn't list the 12832X1 part number I see on Amazon. Same price, same "921" descriptor, though.

12841B2 is the 7440 bulb, which does not fit the Fiat. 12832X1 is the 921 which fits the Fiat.

-Virgil- said:

12841B2 is the 7440 bulb, which does not fit the Fiat. 12832X1 is the 921 which fits the Fiat.

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This is from the "Vision LED Lights" table:
[tr]

This is from the "X-Treme Vision LED Exterior Lights" table:
No part numbers are given there.

Sylvania's bulb guide says the 921 is the appropriate bulb for the '13 Fiat 500, so what's the difference between the two different 921s on Philips' site?

Website error, probably -- I'm going by the '13 and '14 Philips master automotive catalogues, where 12841B2 is the 7440 (W21W) and 12832X1 is the 921 (W16W).

-Virgil- said:

Website error, probably -- I'm going by the '13 and '14 Philips master automotive catalogues, where 12841B2 is the 7440 (W21W) and 12832X1 is the 921 (W16W).

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Strangeness. Especially since the error has propagated to Amazon.com: http://www.amazon.com/dp/B00P2D41OQ/?tag=cpf0b6-20, and the product packaging also has "921" on it.
The 7440 (W21W) and 921 (W16W) have two different filament shapes, so SOMETHING's really weird here.

I wonder if either one would really work well in the '01 Corolla. Seems like these things have a giant chunk of "let's put shadows everwhere" attached to them.

Now this is getting strange. Here is a Philips PDF for the 12841B2, right from the donkey's mouth, that has both "7440" and "921" (and "W16W") listed. The 7440 is physically not compatible with 921/W16W. And here is the sheet for 12832X1. Looks like the same physical item, and at least one of the pictures is the same, but this sheet is incomplete ("Localizer" place holders, etc.).

The 12841B2 comes as a 2-pack for about $23. The 12832X1 comes as a 1-pack for about $23.
Something's not adding up to zero here. And on a hunch I just went and logged out and back into Philips and the product list for these bulbs is "Temporarily unavailable". Maybe some reshuffling going on? I'll have to wait and see what develops over the coming days.

-Virgil- said:

Now this is getting strange. Here is a Philips PDF for the 12841B2, right from the donkey's mouth, that has both "7440" and "921" (and "W16W") listed. The 7440 is physically not compatible with 921/W16W. And here is the sheet for 12832X1. Looks like the same physical item, and at least one of the pictures is the same, but this sheet is incomplete ("Localizer" place holders, etc.).

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INORITE?

From the wattage to the filament shape to the light center length to... well, you get the picture. This is, as they say, "wack".

The 12841B2 comes as a 2-pack for about $23. The 12832X1 comes as a 1-pack for about $23.
Something's not adding up to zero here. And on a hunch I just went and logged out and back into Philips and the product list for these bulbs is "Temporarily unavailable". Maybe some reshuffling going on? I'll have to wait and see what develops over the coming days.

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Yes, that is bizarre. Could explain the "out of stock" on the one item if it can't possibly exist.

For the OP, I'd recommend just waiting for things to solidify before doing the upgrade. I'm still trying to picture how either bulb is a legit replacement for the filament bulb. In my Corolla, it seems the "921", whatever their part number, just won't work because the bulb doesn't come out of the center of the reflector, it comes in off-axis and is in profile respective to the reflector and lens.

Alaric Darconville said:

For the OP, I'd recommend just waiting for things to solidify before doing the upgrade.

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Oh, for pete's sake...there is really nothing unsolid or uncertain here. This new 12841B2 number, we can wait and see what it is, but the 12832X1 is known to be a 921-replacement. It has been for most of a year. I've had a pair of them in my car for a few months now; they subjectively work great. I've also seen a good stack of photometric test data on them in various lamps; objectively they work great. That doesn't mean they'll work in each and every reversing lamp that takes a 921 (W16W), but in many/most of them, they will. Buy...install...forget...move on to next project.

Alaric, my 11' Corolla reverse light was the same with yours, bulb go sideways not pointing straight. I would like to try this Philips but afraid all the light will not be projected well.

-Virgil- said:

Oh, for pete's sake...

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Really?

Hooboy, mea culpa maxima. Edited to fix my typo, which was complicating an already messy number situation put forth by Philips. The known/existing W16W in single pack for $23ish is 12832X1. The new looks-the-same-but-costs-half-the-price apparent 2-pack confusingly and impossibly also billed as "7440" is 12841B2.

-Virgil- said:

Hooboy, mea culpa maxima. Edited to fix my typo, which was complicating an already messy number situation put forth by Philips.

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AHhh, THAT'S where the number came from.
What's annoying about the numbering scheme is that the numbering schemes don't work well to convey what's happening. 12841B2 is actually two of 12832X1 in the same package? I could almost accept 12832X1 and 12832B2 to be "X1 of this, or a Box of 2", with the 1284 being the same, but it seems digits and letters just get modified willy-nilly.

The known/existing W16W in single pack for $23ish is 12832X1. The new looks-the-same-but-costs-half-the-price apparent 2-pack confusingly and impossibly also billed as "7440" is 12841B2.

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Amazon says they'll fill the orders on the 2-pack as soon as they come back in stock. It's tempting to add that 2-pack to the cart, if they'll really perform as well as I'd like. The Corolla's got tinted windows, and though the tinting on the back glass is in great shape and isn't that intrusive, a little extra boost of light would be nice.

The CHMSL also takes the 921, so perhaps it'd be a good fit for that, too. I think the Previa I have uses TWO 921s for the CHMSL, but that starts getting expensive...

At least Philips is consistent in starting their bulb part numbers with the voltage ("12"). But they have re-used numbers for different 12v car bulbs, and yeah, I'm still in a holding pattern waiting for a definitive answer (maybe this week?) from Philips about 12841B2 vs. 12832X1.

Don't use this bulb (under either part number) behind a red lens -- it's a "6000K" cold white that doesn't contain enough red light to make the red functions "pop"; the color winds up being a sort of brownish-pink. That's one thing about those Sylvania "Zevo" LED bulbs, is that the warm white "3000K" variety makes a perfectly fine red color when used under a red lens. Those bulbs have other (big) problems, though, and there's no W16W/921 replacement in the product line.

I have some test data (not sharable, sorry) that shows some reversing lamps giving objectively better performance with the Philips LED than with the original 921 (W16W). A neat trick! It will be good to know what range of bulb angles this holds for.