i dont know if there's a book or website where we can find out how a car is developed.

How about this:
vehicles have different systems in it e.g.

Brake system, Engine, Cooling System, AC, electrical system, steering and suspension, transmission, emmision systems. ..meron pa ba?

 so..
for each system, there should be someone(one or more persons) in charge of doing research regarding the parts needed for that particular system. they provide the specification to the buyer.
while determining which parts to use, they interface with one another just like how those systems interface in the complete vehicle. so that they can match with each other.

enrico...how is this done in your company?