re: Simple diode question in a circuit

I have 3 circuits in my truck wired to function like what you want.



I used on-off-on switches to designate which voltage source supplies each relay. Did a circuit for Offroad Lights, Auxiliary Reverse Lights and interior accent lighting.

Gave me control to select between:

Auto-on with _____ function
.
.
OFF
.
.
Always ON (switched)



Here's some picts of the rest of the setup. Gets a little more complex since I wired in the LEDs on the switches to indicate which position it was in, but I love messing with stuff like this.