maybe the differences are in fact about whether or not a connection for the courtesy light is included in the "safety package" equipped versions ONLY of the harnesses. A convertible or Coupe (coupe with a roof console) car could use the same harness without any trouble but a fastback or coupe with the roof dome light could use the same, right? I wouldn't know either way since I have no convertible example, no fastback example nor a coupe with a standard interior example to compare anything. My suspicion is that they can all use the version of wiring harness than includes the dome light wire, just would leave that disconnected on cars not needing to use it (e.g.: The image of the "unknown wire" seen in the image located in the other thread I referred to in the initial post) That wire (in the other post) was labled as "unknown" but again, this was for an example WITHOUT the safety package AND was stated as out of a convertible which, according to the MPC, is correct for all 3 body types if no safety package is on the car..
I think that perhaps the focus on the interior lighting is not pertinent. Two reasons: (1) The base 14405 of the MPC states that it is good for all three body styles, (2) the alternate 14405's (two total) are related to "safety" (which as I stated previously is probably convenience control), and not lighting.
There is no mention of interior lighting.
To have unused lighting connectors behind a panel for a coupe with no overhead light, and for a convertible, is not really a problem.
I do recall looking at some dome light coupes and the main harness connection for the light, compared to the overhead console, is the same as you speculated.
Perhaps A.M. leaves out the dome/overhead console wire in their convertible versions. It looks like that would not be technically correct, but would not hurt nor be noticed.
To me the question is - what is the difference between the FB and others for the convenience control option. All I could think of is where the fuel level sending unit wire comes off main harness - might be in a different location?
I think you will be looking at this: AMP Taillight Wiring Harness With Low Fuel Warning Coupe/Fastback 1967