This is about the red charge light on the headlight shell just behind the speedometer.
that is connected between the battery and the generator. This light bulb
burns at its rated value when there is 6 V across its terminals. That is
why it lights up when the generator is not generating. It then, effectively,
is connected to +6V from the battery and 0 V from the generator, so it
the indicator has +6 V on one end and +6 V on the other: no voltage
difference, so it doesn’t light.
However, if the generator output does *some* power, but the voltage isn’t
adequate, the voltage difference across the indicator will be smaller than
6 V. It might burn softly, but it will be very hard to see. This is typical
for light bulbs: if connected to half their rated Voltage, they burn at 1/4
power, and thus approximately 1/4 light output. Do the math: if connected
to 1/3 the voltage, it will burn at 1/9th power.
It will be very hard to see, especially when there is ambient light, as on a
From this one learns: the red light will indicate that you are using
battery power, for example, when you are about to start the engine and have the key
It will NOT indicate discharge during riding the bike when the
generator/regulator is “just not up to it.” You might be slowly depleting
the battery and the indicator will not light.