The bulb may measure 20 ohms cold but it will be more like 200-500 ohms hot. If you install a 20 ohm resistor, the 7.2 watts that is disipated would fry your eggs quite nicely.Originally posted by JimM:
By brown generator wire, you mean the one that used to be for the "alt" idiot light? This wire is an "exciter" for the alternator. If it is not attached to +12v through a 20 ohm resistance (the bulb) the car will not charge.