An obvious but quite distant connection - Solved by a few Americans (North & South) and a Briton.

[streamliner]

Just a guess to open this up to more successful puzzlers:  The 1937 P4 in "Doomed to Die" (1940)?

[Ray B.]

Not that one. The Plymouth in this film is a convertible. The one we're talking of is a Coupe, as you previously guessed. We've had The Big Sleep in one of my recent group puzzles, so this one should be easy to check.

I first was sure that it was a 1937 model, but it appears that the character drives a 1937 in some scenes, a 1938 in others. Apparently the studio had a couple of cars and used them interchangeably.

[streamliner]

Ahhhh...  Then I'll go with "High Sierra" 

[Ray B.]

And you'll do well. High Sierra it is. Now you  can move on to Character B.

[João]

Link number #8 ( The engine picture ) is a 1937 Lincoln Model K Sedan by Brunn.

[Ray B.]

Correct. That engine bay is that of a 1937 Lincoln model K. Maybe a sedan, I don't remember, but the car I'm after is not a sedan.
Links 7, 8 and 9 are locked for Joao  24 hours (as often with connection puzzles, this part is becoming rather complicated. Sorry).

[João]

You´re looking for a "Parade Phaeton" by Willoughby?

[barrett]

This is the most incredibly complex puzzle i've ever seen..... Am I the only one whose brain has been slightly fried by trying to work out what's going on here?? 

[Ray B.]

You´re looking for a "Parade Phaeton" by Willoughby?

I am not sure if it's by Willoughby or LeBaron, or if the true denomination is "Parade Phaeton. But I am sure that it's a phaeton, in other words a convertible sedan.
This link is locked for you 24 hours.

@barrett: Not as complex as you think, maybe. For instance, a good guess at this link (N°8) and an identification of the man you can see in link 6 will unveil link 7, and so on.

Now once your brain has reached the right temperature, you could be able to finish solving this one by Otto.
http://www.autopuzzles.com/forum/index.php?topic=13287.0
Take a look at his last "clues" (that's what he calls them., some nerves). That's what I call a brain frying puzzle!

[João]

uhmmm....This Lincoln is associated with a Song or something like a Movie too?

[Tom_I]

This is the most incredibly complex puzzle i've ever seen..... Am I the only one whose brain has been slightly fried by trying to work out what's going on here?? 

You are not! 

[Ray B.]

uhmmm....This Lincoln is associated with a Song or something like a Movie too?

I'd say you begin to know me. A movie, let's say (by the way, the song is great too. I've been looking for that record for years.)

[Tom_I]

Ah, at last I'm beginning to get my slightly fried brain around this puzzle.

I think I now see the significance of Ray's comment about "Character A (or C, it doesn't matter)". The series of links is symmetrical, and can be solved from either end.

So what happens at one end, happens in reverse at the other end.

I can't work out the middle yet, but going from the Lincoln Model K, the next link must be its hood ornament, which in this case is a greyhound.

Then the next link (vehicle) is a Greyhound bus.

And finally Character C is Carl Wickman, founder of Greyhound Lines Inc.

[Ray B.]

Fine thinking, Tom! This a symmetrical puzzle indeed, but I didn't fry my own brain enough to assemble this. So it's longer on one end than on the other.

Now the photo for the last character ( captioned Connection #1) does not come from the internet. But there are other ways to find who he is.

[streamliner]

Any chance that Connection 1 is crime writer Robert B. Parker, who seems to basically have continued Raymond Chandler's work (and also created Spenser For Hire)?

[Ray B.]

Not Robert B. Parker, but you're on the right direction.
Here's what we have now:

Character A (or C, it doesn't matter): Christopher Jones (Joao), Captain of the Mayflower, played by Spencer Tracy (Otto Puzzell)
Link 1 (vehicle): The Mayflower (Joao)
Link 2:  Plymouth "Mayflower" hood ornament (Joao)
Link 3 (car):  1937 Plymouth DeLuxe Coupe (streamliner)
Link 4: High Sierra (streamliner)
Character B (picture "Connection 1):         
Link 5:
Link 6 : John McIntire (Aaron 65)
Link 7: Honkytonk Man (Joao)
Link 8 (car) 1937 Lincoln Model K convertible sedan (Joao)
Link 9: Lincoln "greyhound" hood ornament (Tom_I)
Link 10 (vehicle): A Greyhound bus (Tom_I)
Character C: Carl Wickman, founder of Greyhound Lines Inc. (Tom_I)

[Aaron65]

Link #6 looks like actor John McIntire, from the movie Winchester '73 maybe???  He played Joe Lamont in that movie.

[Ray B.]

You've got a good eye. It's McIntire indeed in Winchester 73. And the link here is the actor, not this particular film.

[Aaron65]

John McIntire is buried in Lincoln County, Montana.

[streamliner]

John McIntire played "Grandpa" in "Honkytonk Man"

[Ray B.]

He sure did. Now can you trace how he can be linked to "High Sierra"?

[Aaron65]

I'm going to take a stab at Link #5...How about John Huston, who directed McIntyre in The Asphalt Jungle, and also cowrote and directed High Sierra's screenplay, with W.R. Burnett...I'm not sure if Burnett is Character B though...I don't think so.

[Ray B.]

Aaron, you're almost home. Link#5 is "The Asphalt Jungle". But John Huston is not in the picture.
Here is another picture of Character B / Connection #1.
Locked for you 48 hours.

[Aaron65]

That's W.R. Burnett, who wrote High Sierra and co-wrote the screenplay for the film...

[Ray B.]

It sure is Burnett (who had lost some weight since the first photograph). This last one is the sole picture of him I could find on the internet.
So we can consider that the connection is established between Christopher Jones and Carl Wickman, with all the links found.

Character A (or C, it doesn't matter): Christopher Jones (Joao), Captain of the Mayflower, played by Spencer Tracy (Otto Puzzell)
Link 1 (vehicle): The Mayflower (Joao)
Link 2:  Plymouth "Mayflower" hood ornament (Joao)
Link 3 (car):  1937 Plymouth DeLuxe Coupe (streamliner)
Link 4: High Sierra (streamliner)
Character B:  William Riley Burnett (Aaron 65)      
Link 5: The Asphalt Jungle (Aaron 65)
Link 6 John McIntire(Aaron 65)
Link 7: Honkytonk Man (Joao)
Link 8 (car) 1937 Lincoln Model K convertible sedan (Joao)
Link 9: Lincoln "greyhound" hood ornament (Tom_I)
Link 10 (vehicle): A Greyhound bus (Tom_I)
Character C: Carl Wickman, founder of Greyhound Lines Inc. (Tom_I)

It's not gonna be easy for me to make the points count. For instance, I'd say that although Aaron 65 identified John McIntire he didn't explain wha t he was doing in this puzzle, something that was established by streamliner.
I'll think this over and will make a proposal later to all the puzzlers who helped put the pieces together.