In normal operation, all the power for the lighting comes directly from the key. When the key is in RUN;
- power from the key goes directly to F12, enabling the brake lights, the alternator lamp, and the directional turn signals.
- when the lights toggle switch (1st position) is flipped up, power is enabled to F3, which turns on the running lights markers (up 6 for Euro cars, 8 for US cars), and the dash lighting. Gauge brightness is thru the rheostat, the #2 toggle, but the ring lighting at the cigarette lighter (and the indicator lamp in the Tach) are not affected by the rheostat.
And now, you can use the trunk light 
