Help with ignition light and alternator please

[Vic Butler]

The ignition light extinguishes when the voltage on both sides of its wiring is equal, nothing to do with polarity. An LED bulb behaves the same but draws insufficient current to excite the alternator.
From memory the 2 LED headlight bulbs in my Series 3 Land Rover draw about 2 amps each so a much lower wattage LED bulb like the ignition warning ligh won't draw enough current to excite the alternator unless a resistor is in the circuit.
The standard filament ignition light bulb draws about 2.2 watts, equating to about 0.185 amps (watts = volts x amps). An LED bulb will draw about 0.09 amps, or maybe less ,about half of the filament bulb.

[Bumpa]

Thanks Vic and Charles. You are right of course.