Refer to the Diagram: Switch “SI” is in the “on” position but “LI” light does not come on. Voltage across “LI” is 120 volts. Voltage across “SI” is O volts. What is the problem?

Refer to the Diagram: Switch “SI” is in the “on” position but “LI” light does not come on. Voltage across “LI” is 120 volts. Voltage across “SI” is O volts. What is the problem?