Bulb not lighting up if resistor is used
I found a reference to a #13 radio pilot lamp rated at 3.8 volts, 0.3 amp.  To operate that lamp from a 12 volt supply, you need a resistor that will drop 8.2 volts at 0.3 amp.  Ohm's Law says that a 27 ohm resistor would work.

If your lamp draws a different current, the you would need a different resistor, but 27 ohms should be a good starting point.