Resistor size needed

Discussion in 'General Electronics Chat' started by star71981, Sep 30, 2016.

  1. star71981

    Thread Starter New Member

    Sep 30, 2016
    I'm trying to add a resistor to the positive parking light wire on a led 1157. 12volt car. I want to dim the parking light bulb so when I use the brake or turn signal I can notice the difference. Right now the brightness is about the same between the parking light and brake light on. I don't know what size resistor. I was going to cut the wire and add the resistor. I've tried a 50w 6 ohm resistor used for hyper flash and it changed it very little. Thank you. I was thinking a 400ohm. But what wattage 1?
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Watts = V^2/R
    Where V = voltage and R = resistance
    and triple the calculated value or more for a safety factor/to keep the resistor from running too hot..
  3. panic mode

    Senior Member

    Oct 10, 2011
    that is LED bulb drawing some 0.18A

    no wonder 6 ohm didn't do much. 400 Ohm will turn it off completely.

    you may want to try to cut that down by maybe 50%.

    12V / 0.18A = 67 Ohm (this is bulb alone)

    so something in order of 30-60 Ohm may do depending how much of a dimming you want to see. 5W resistor is ok