Resistors and Adding LEDs to Fanbus

[NotSoSimple]

My dad gave me a breadboard with a bunch of LEDs and resistors soldered on. I desoldered everything on the breadboard, and have tested the LEDs to work. Now I was reading about you need resistors if your going to run the LEDs on 12v. How do I tell what resistor is what?

Also, I already have a simple Fan Bus. 4 Rocker Switches (On/Off) With my fans and my blue cathode on the switches. How hard would it be to integrate the LEDs so when a fan is on, the LED lights up?

 

[Steak]

ON position of the switch terminal---470 resistor---LED '+' side; LED negative --->ground

 

[NotSoSimple]

Do I solder this all on a breadboard or do I just use wires. Also, whats the leeway in resistor Ohms? Could I go higher in Ohms than 470.

And about the previous thread, I already found the Ohms of my resistors.

 

[matoch]

Take a look at the case mod FAQ there are a couple diagrams and a link to a page where you can fill in the supply voltage, diode voltage and the diode's rated current and it will tell you what resistor to use.