Linking headlights to interior light

[particlewave]

Meir: yeah, I'll check as well before I stick my foot further into my mouth.
It's been a while since I worked on that circuit, but that's how I remember it and that what I see in the diagram.

Edit: confirmed. Using the cig lighter as a constant source of 12V+ and ground, the courtesy lights definitely have a constant 12V+ and the ground is switched.