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Old 06-23-2008, 04:17 PM   #4
Mulder
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Join Date: Oct 2001
Chapter/Region: Tri-State
Location: NYC
Vehicle:
02 RAV4 MT
15 WRX/11 CRZ

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You'd have to do an Ohm's Law calculation based on the nominal current of the LED and the supply voltage. In this case, using 12V and 20ma, R=E/I so R comes out to 600 ohms. Allowing for higher voltage when the car is running, say 14V, makes it 700 ohms. You could probably go to 1K ohms for safety and not see much difference in the brightness of the LEDs.
As for where to install the resistors you'd have to wire them in to the circuit someplace, if you're sticking the LEDs in the bulb holders there is no place for them there.
There may also be premade 12V LEDs with integrated resistors that you can use for this application, if so that's a better way to go. I'm sure if you search the many threads that already exist on this topic you'll find more info. There's a sticky thread in this forum and also in Interior/Exterior.
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