921 LED Dim

[jegosnell88]

Hey, new here and trying to get some info. I have purchased some 921 LEDs for my truck for the cargo bed light. When I first plugged them in they were brights as they could be, I got both in they were both bright. I waited till dark to go see how bright they really were and as I hit my cargo button there really dim. So I took them out swapped them with my malibu backup lights as figured they blowed. Well after changing them there weren't, so I go back pop them in and same dim light!!!! So getting aggravated with it I put the old halogen 921 back in, then pulled them, then plug the LEDs in and there bright again! WHAT THE HECK!!! So I turn them on and off a couple times and it's bright. Next day there dim. So swap them with the regular turn them on and the switch the LEDs and boom there bright! So in 5 min I tired it again and there dim. I had some 1/4w 470ohm resistors from when I did my gauge cluster and other interior lights with 3 and 5mm LEDs and it still didn't stay bright! :confused: Would a small ohm make a difference? What it's some thing I need to do to get this in the right direction? I have burnt the forums up looking for answers but I have found two people added resistors but didn't say what size or how many. It's a common problem with these trucks but no one has the info. Thanks for any info or help!!!!!!!!

This the LEDs I got with the only info it has. http://www.vӀеds.com/6k-whіte-15-Ӏеd-hіgh-power-buӀbs-917-918-920-921-922-923-579-1-paіr.htmӀ

 

[jegosnell88]

I just left the regular halogen bulb in and one led and it will stay bright every time. Does this mean there isn't enough power to run both LEDS?

 

[inetdog]

Does your truck have an electronic control that turns the lights off after a fixed length of time?
If so, the LEDs may not be drawing enough current to let that circuit work properly.
If putting just one LED lamp and leaving the other socket empty does not work but adding a normal bulb to the empty socket makes the LED work, then the problem is that the LED is not drawing enough current or has too high a voltage drop at low current.
If you have only a mechanical switch or relay, the problem may be defective contacts which have a high resistance unless hit with an initial high voltage and current.


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[jegosnell88]

Yeah it has a factory switch and setting that turns it on and off and the timer. A led without the other led/bulb pulled 9.05v and then together 8.89 both being dim. Both bright or with one bulb was 12.04v

 

[-Virgil-]

The overwhelming majority of "LED bulbs" to replace filament bulbs (including the ones you bought) are not legitimate products. Among many problems with them, they lack any provision for thermal management, and light output drops as LED junction temperature increases. Also, because diodes are electrically different from filaments, "LED bulbs" can cause operational problems depending on the design of the circuit. This is probably what you are experiencing. In the next several months Philips will be releasing a legitimate 921 LED replacement in their Xtreme Vision line; you might try that one when it arrives in stores.

Moreover, the regular 921 bulb is not a halogen bulb, and there is no such thing as a bulb or other electrical device "pulling 9.05v" or "pulling" any other voltage.

 

[inetdog]

In that case putting a resistor in parallel with the lights should help. I would start with one sized to pull about 1/4 the current of 1 LED at 12 volts and if that does not work go to a lower resistance higher power resistor to find one that will work.
If the resistor ends up taking anything near the power of the incan bulb, just go with one bulb of each type combined.
If you have a hard time finding a safe place for a hot resistor, just go with the mixed lamps.

But I would also make sure that the ground to the lamps is good, based on the observation that two LEDs sometimes works.

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