Hey Dave great information,
personally I would never put a resister in parallel with the charge light. The charge light is the first port of call on your charging systems health. If you "gen" light didn't come on when turning your ignition on it should be investigation straight away and the assumption shouldn't be made that the globe is just blown the resister will keep things working because 9 out of 10 times it won't be the globe, it will be a charging system fault.
On most alternators the alternator warning light provides excitation by having ignition on one side of the globe, that power passes through the globe down to the D+ wire on your alternator which in turn connects to your rotor positive brush, that signal then goes through your rotor out the negative brush through the regulator then to earth turning the light on and providing a slight magnetic field for initial charging. This in turn informs you if the regulator, brushes, or rotor coil are functioning correctly, any fault that will not allow the light to turn on.