led modding help

I just did a mod on one of my 2 xbox consoles and i put red leds in the top so the jewl would glow red and so i came to my other one and i wanted it blue i have 3mm blue leds 3.5v 40mA and i was using 8 of them but when i modded it all up and hooked it up to power(molex) the leds lit up bright and then burnt out one by one and im not to good with working out resistors and all the calculators iv been to arnt much help at all. So i need to know what resistor should i use to lower the current flowing through a little so they dont fry every time

Cheers

 

You need to post the specs of the leds.

Also which leg are you feeding from the 12v or the 5v?

 

I only got a little slip with the leds on what they are it has on it:
RED light emitting diodes 3mm
Tested to 50mA current
1volt to 4.8volts 50mA

I was hooking up 8 to the 12v which goes to the hard drive (molex cable) i was hooking the longer end the positive leg to the positive coming out of the molex

 

Use the 5 volt leg and a 15 ohm 1/2 watt resistor they are a buck for 5 at radio shack.

 

Did you hook them up series or parralell?

 

Google led calculator you get something like this.

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

Use common sense, you're not going to be able to run a 4.8v led from a 5v source without a resistor.

Here's a pretty good writeup http://www.llamma.com/xbox/Mods/xbox_jewel_led_mod.htm