I've been thinking about this recently. I'm nearly certain that door switches for the dome lights was an option. I found it in the 1975 brochure. I also wondered why I had this random green wire all by itself outside of the main wiring harness. It's like it was an add on. I noticed the fancy map light and cruise control are wired the same way. A mini harness outside the main harness. I wasn't happy when I discovered the map light has zero fuse protection. It hooks up directly to the main six terminal always on Packard 56 connector. All my door switches are installed now and working great. The passenger side got the GM style with the 3/8-24 thread. The drivers side used the 1/4-20 version. The GM style is nice. More robust. I used clear vinyl on both leads to prevent it from accidentally grounding to the body within the cavity.