Ho yes, i understand now !! It is standard 3 or 5 mm yellow pannel LED. On my layout power is provided by a 24 Volts industrial power supply. So i use 1K ohms resistor. If you use standard 14 V from a power pack, better is to use a 640 Ohm resitor.
The law is U=RI
U tension in volts
R resistance in ohms
I current in amps.
So if you want to have the R value, you use this law : R=U/I
I is the current dropped by the Led (Cf data sheet of the component you have chosen) ,
U the tension provided by the power pack.
You bring the nearest upper resistor value you will find in electronic store.
For pannel LED (20mA) 1/2 Watt power is enouth.
If you chose Hight luminosity LED (droping 30mA to 50mA) better is to purchase 1 Watt power.
Never use 1/4 watt !! Too Hot
For polarity it is very simple : if it's work polarity is ok. If don't work polarity need to be inverted.
Resistor is mounted in serial, one resitor on each LED.
My two cent's ...