Paul__B:
Might I add that this may want to be temporary.
I've never been involved in the development of a product that hasn't had a power on LED. Many of the products I've helped build have also had a little button that can be pushed to force an illumination of the LED so that it could be tested to make sure it wasn't broken. Power on LEDs are a good idea.
knut_ny:
12V -> LED anode.. LED cathode(flat side) .-> resistor.. resistor -> 0V (GND)Resistor value 1000 Ohm +/-
Exactly. I would add that the way to calculate this is
R = (V - 1.7)/0.01
where R is the resistor value you want to calculate, V is the voltage - in your case 12 - the 1.7 is the voltage drop across a LED (the ones I use anyway so check your data sheet), and 0.01 is the amount of current (10 mA) it takes to illuminate the LED (again check your data sheet). So in your case:
R = (12 - 1.7)/0.01 = 1030
So knut_ny was on the money.