I need some help on lil project for my car.
I'm trying to wire LED bulb from Fuse Box.
but I forgot how to calculate resistor
trying to go over stuffs from freshman circuits book but hmmm.
I just need to get number for resistor.
any expert here?

also, I never done it before but I can get power from fuse box right? does it matter if I tap the wire from 20A, 15A?
hope I'm not missing any point.

 

yes, does not matter where you tap in 10A or 20A fuse. does not make any different.

the formula to calculate R is correct, R~ 300 ohms is fine.

 

Banana, thank you very much

 

hmm I can't make it to work yet.
I test with 12v( AAA x 8) and it's workign fine but when I install via fuse(I soldered on top of fuse of 15A), can't make it to work.
maybe ground is bad.. time to get multimeter. meanwhile any idea what I'm doing it wrong?

 

I assume you got the polarity right if you battery test work.
so either you did not have any power at the fuse where you soldered or you dont have ground, you can always test using a test light or volt meter