4.5V LED's in a 12V system ?

Since it's been years since I did anything like this *sigh* ok how do I use the blue LED's from Radioshack that are rated max 4.5V or 6V ? What I want it for is this, hook up a manual on/off switch for the radiator fan, and then hook afterwards hook up a separate LED to the switch. After that I plan on adding more LED's hooked up to switches (fog lights etc), but I need to get over this first obstacle. How do I drop 12V down to 4.5V or 6V ? Also what about brightness ? I've been looking at this two: http://www.radioshack.com/product/index.jsp?parentPage=search&cp=&productid=2102850&kw=blue+led&tab=techSpecs http://www.radioshack.com/product/index.jsp?parentPage=search&cp=&productid=2102851&kw=blue+led&tab=techSpecs What brightness would I need ? I'd like it to match my reverse glow gauge faces. Olaf

San Diego, CA

 a 50 ohm resistor will cut your voltage by one volt so adjust accordingly to get to the rating of 4 to 6 volts. they usauly run at 5v but that is how you will adjust the brightness of the led by increasing or decreasing the voltage inbetween those ratings. radio shack has what you need .JUST ONE MORE AMP!!!

hu,alpine cva 1005/dva 5205

sound processor,symmetry(first one).

sub amp,power 1000 the terminator.(1992).

subs,spl comp dual 1 ohms.

punch 150hd on a 10" ev.

alotofhighs

ok if the leds are 4.5volts, and getting that from 12v, u need a 360ohms resister (will run at around 4.62v) now as for brightness, if they are in ur few so u can tell they are on u DO NOT want bright ones, go for high brights maybe even run more resistance so its not so bright (390ohms will run at 4.2v), anywho, good luck with thismodest yet effective... ECLIPSE 12", Venom 8"x2, Focal 5 1/2" comp.,Response amps x2 (580WRMS total @ 4Ohms), Pioneer TFT + DVD, good for 148.7dB