There are some illuminated switches that operate without a neutral. For a lamp that is lit when the switch is ON, I can envision a circuit diagram that has the switch lamp in series with the switched circuit. But this would create significant additional resistance in the current flowing through the line to the main load. If the switch is parallel to the line, virtually no current should flow since the resistance to the lamp is so much higher than the completed switch circuit.
For switch lamps lit in the OFF position, a switch lamp in series would allow a trickle of current through the actual load, causing a dim glow in a fixture or some current in a motor. This seems wrong.
How do no-neutral illuminated switches work?