Originally Posted by Monkeygrits
You could run the switch power wire to the headlight power I guess and leave the switch on achieving what you want.
If he is going to do that and leave the switch on and that would work, he wouldn't need the switch and he could do all the wiring under the hood.
OTOH, I KNOW the guys replacing the headlights with HID's had to be careful and add some resistors so the car didn't think a bulb was out. Not sure if a vampire tap to activate a relay would cause any issues, but I think it's conceivable.
In some ways the car is actually MORE sophisticated than you would prefer.