I just replaced my map lights with festoon LED bulbs.

When I turn one on it only comes on very very dimly. If I turn the second one on at the same time they both light up full brightness.

Do I need to add a resistor in somewhere so I can turn a single light on and off without having to turn them both on?

 

Resistors are needed. There are various online calculators you can plug in your numbers to find what you need to use

 

Or I can do the math myself.

Does the resistance of the LED have to be equal to the bulb that WAS in the socket prior?

I'm thinking I can just drop in a resistor beside the festoon bulbs, or solder a resistor to the festoon leads.

 

Yes you need a resistor.

Measure resistance of one of the LEDs you have now and match resistance.

 

I can't get a reading on the festoons.

 

get the reading when they are plugged in & turned on buddy

you need current to read resistance on a diode.... :-P

 

*facepalm*

that is first semester stuff.....

in my defense, I haven't measured a diode since then

 

lol all good bud... I cant tell you I have a hard time remembering all the Calculus and even some of the efficiency calculations and what not, but I kept all my important textbooks and notebooks so it's all good


You can get a resistance reading over a diode if you have a nice fancy multimeter that has the ability to generate voltage to measure resistance across a circuit... they are usually more accurate too.

Anyways go measure and try a resistor that matches....

 

I kept all my stuff for the same reason, I'll never remember half of this stuff lol.

So I need to match the resistance of the LEDs bulbs I'm using?? the original bulbs measured around 2.2-2.5Ohms, but I'm thinking I should check the current draw from them, measure the actual voltage of the truck and calculate the resistance.

I guess I just don't understand why the resistance of the LEDs need to be matched with a resistor. Shouldn't I be trying to achieve the resistance of the original bulb?