Why does my fluoresent light power line show 15 volts with switch on and off?
Are you sure that it's a ballast resistor and not a transformer? A resistor would be extremely inefficient, obviating any benefit in efficiency of a fluorescent lamp.
A DVM has a high input impedance and will pick up stray voltage coupled by wiring capacitance even when the switch is off. There is no need to measure the voltage when the light is switched off.
N.B. Do not measure the current across the mains with the meter. If you put the meter in series with the lamp, it should draw no more than 1 ampere, but do not put the meter, in current mode, directly across the line!


If you're having frequent issues with the fixture, replace it with a surface-mount LED fixture. You can find theses in different color temperatures from 2,700 K (co0lor similar to incandescent) to 6,000 K (actinic blue-white). LED lamps should (at least theoretically), last many years more than fluorescents. (The link is just an example.)