Linking headlights to interior light

[geraintthomas]

Parking lights with courtesy lights. When the courtesy lights come on, I wanted the parking lights come on too, so that your tail lights, number plate lights and front parking lights illuminate. But I wouldn't want the switch to turn on the courtesy lights if I switch it to the parking lights position, if you see what I mean. So a diode would be needed.

I just thought "Oh! I'll just bridge the 12v from the courtesy light feed to the parking light feed with a diode, so the parking lights don't switch on the courtesy lights, but the courtesy lights do turn on the parking lights whenever the courtesy light is on". But as particlewave said, the courtesy lights have a switched ground, whereas the parking lights have a switched positive. If they were both the same, it would be that easy.

I thought about jumping the fuses but, there's a separate fuse for each bloody bulb. So that wouldn't work either.