Voltage is applied at all times to the light 1 relay. When the light switch is turned to PARK/HEAD, ground is supplied to the coil of the light 1 relay. When the power and ground are applied to the coil of the relay,

When the power and ground are applied to the coil of the relay, the coil is energized and the contacts are closed.

Voltage is applied to the illumination controller and all of the illumination lamps.

The lamps are grounded through the illumination controller. Because the illumination controller is grounded through the junction block at G203, the illumination lamps light when the voltage is applied.

The illumination controller determines the brilliance of the lamps by controlling the amount of current applied to the lamps as you turn the knob either clockwise (more current) or counterclockwise (less current).