could you tell me why the diodes are facing the way they are (lines on the left)?
it's indicating current flow as it's depicted on the diode. The current from the 2 sources will be flowing into the switch, but not allowed to flow the other way, so you wont have your dome lights on while your car is on, and you won't burn the wiring for the dome light up while trying to power all the ign switched devices...
1991 Chevy Suburban 1500 w/SBC 350
2005 Saturn ION 2 sedan