led dome light resistor
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Record Breaker
Joined: Dec 2009
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From: Ontario Canada
led dome light resistor
So i got the cheap led's off ebay for dome light (all 3) and they sometimes flicker or half will come on. i think its because the truck thinks its off so it keeps it off (just guessing) because if i but 1 normal bulb in it all works perfectly
my question is does anyone know the resistor i need to make this work and is it in parallel or in series?
p.s i did a search and couldn't find it also my other thread wasn't going anywhere lol
my question is does anyone know the resistor i need to make this work and is it in parallel or in series?
p.s i did a search and couldn't find it also my other thread wasn't going anywhere lol
Moderate User
Joined: Oct 2008
Posts: 17,003
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From: Albany, NY
You need to 2 know the specs of both bulbs before you can figure ut what resistor to use. You need to know the current draw of the halgen bulb and compare it to the current draw of the LED.
My guess is the current draw for the LED is practically nothing and is causing the on/off of the lights. I would try between a 60-100ohm 1/4watt resistor across the contacts. Meaning stretched across from one side of the bulb terminal to the next, just as the light bulb does. This will draw a little more current and should keep the lights on steadily.
60ohm will add 200milliamps= .2A ans 100 will give only 120milliamps = .12A
Running the resistor from one side and grounding it out will do absolutely nothing. Current will flow through the easiest route which won't be through the resistor that's just grounded out, there needs to be sucking power from the otherside such as the bulb. You could cut the lead wires and wire in the resistor in series as well which is te best route here, but there is cut/splice involved. <<<---You may have to cut/splice if the accross bulb trick don't work because you are essentially changing the current at that point and you may actually reduce it due to running parallel with the bulb?? Resistors ran in parallel reduce everything but voltage.
My guess is the current draw for the LED is practically nothing and is causing the on/off of the lights. I would try between a 60-100ohm 1/4watt resistor across the contacts. Meaning stretched across from one side of the bulb terminal to the next, just as the light bulb does. This will draw a little more current and should keep the lights on steadily.
60ohm will add 200milliamps= .2A ans 100 will give only 120milliamps = .12A
Running the resistor from one side and grounding it out will do absolutely nothing. Current will flow through the easiest route which won't be through the resistor that's just grounded out, there needs to be sucking power from the otherside such as the bulb. You could cut the lead wires and wire in the resistor in series as well which is te best route here, but there is cut/splice involved. <<<---You may have to cut/splice if the accross bulb trick don't work because you are essentially changing the current at that point and you may actually reduce it due to running parallel with the bulb?? Resistors ran in parallel reduce everything but voltage.
Last edited by dirtydog; May 28, 2010 at 10:00 AM.
Champion
Joined: May 2008
Posts: 4,210
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From: Shreveport, LA
Dog I think you might have to run it parallel through the bulb, if its just laying across there the resistor will draw a current and the LED will draw a current, but I dont think the resistors draw will lower the current enough.
It will be easy to try it, if that doesnt work just tie it in parallel
It will be easy to try it, if that doesnt work just tie it in parallel
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Joined: Jan 2007
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If the LED isn't drawing enough current, you need to add more load to the circuit. Running a resistor in series can only reduce the current (more resistance, less current).
On the other hand, the halogen sucks a *lot* more current than LED. You need to draw enough current so the PCM will think there is something there. The problem is, the normal 1/4W resistors really can't take much before they burn out. 1/4W at 12V is only 20ma. Or, flipping it around, you'd need at least a 600ohm resistor so you wouldn't burn it out. I'm guessing that wouldn't be enough to fool the PCM.
You can get larger wattage resistors, but they are significantly larger than "normal". a 1W resistor would probably be bigger than the original halogen bulb.
As silly and low-tech as it sounds, you might want to consider getting a low-wattage bulb (but enough to fool the PCM), paint it black and run it in parallel.
On the other hand, the halogen sucks a *lot* more current than LED. You need to draw enough current so the PCM will think there is something there. The problem is, the normal 1/4W resistors really can't take much before they burn out. 1/4W at 12V is only 20ma. Or, flipping it around, you'd need at least a 600ohm resistor so you wouldn't burn it out. I'm guessing that wouldn't be enough to fool the PCM.
You can get larger wattage resistors, but they are significantly larger than "normal". a 1W resistor would probably be bigger than the original halogen bulb.
As silly and low-tech as it sounds, you might want to consider getting a low-wattage bulb (but enough to fool the PCM), paint it black and run it in parallel.