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Thinking of switching all 4 turn signal lights to LED from halogen and I will more than likely need some resistors due to notorious hyperflash or LEDs with built-in resistor as I prefer not to splice any wires.

Then I realized the 2 front signal lights stay on when the headlight is on and I am assuming this is going to load the resistor constantly at night time, causing it to heat up. I am curious to know if there is gonna be enough heat to melt the plastic of inner housing.

Also can someone explain what does the rating of a load resistor tell? If it's rated at 6 ohms and 50 watts, does that mean it's gonna consume the same watt as 50 watts light bulb does?

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The power rating of a resistor is how much it can dissipate continuously, and being a "power resistor" that would be at a surface temperature of perhaps 150 °C.

To find out how much power it is actually dissipating, you would need to know the current through it, or, more easily, the voltage across it, when the lamp is on.

To calculate the power dissipated by the resistor, use the formula P = V² / R. If it turns out to be something like 3 W then it is unlikely to get hot enough to cause damage.

  • Thank you for your explanation! Since most cars generally have 12 volts so I am guessing it would be 22-25 watts – user49767 Jun 17 at 15:53
  • @user49767 The thing is, you have to measure the actual voltage directly across the resistor, because it won't be 12 V as some of the voltage is dropped across the lamp. I guess that as you can see the rating of the resistor, you can see its leads. Do you have a multimeter? (Always be careful measuring electrical things in a car in case the probe slips and welds itself to something.) – Andrew Morton Jun 17 at 17:54

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