Everybody who has ever driven in a car would think that they could build one. This would result in fierce competition for jobs on the assembly line, which would require that aspiring auto workers would have to prove themselves outside the industry before they were hired. Some would work their way into the industry by working on toaster or radio assembly lines. Others would tap their friends and family and max out their credit cards to produce a car themselves, which they would then take to indie auto shows in the hope of impressing a suit from Detroit with their ability.
Once an aspiring auto assembler had built a personal buzz in this way, he or she could expect interest, and possibly offers of employment, from auto manufacturers. At this point, the auto worker would be wise to get an agent, a person who would take 10 per cent of their paycheck to find the best offer among those the worker him or herself had generated. If there were enough competition among auto manufacturers for a particular worker, the agent might be able to negotiate a contract that offered greater incentives than the industry standard.
Owing to the fierce competition for positions on the assembly line, the people who actually were hired by auto manufacturers would, for the most part, be those who were the most persistent and/or aggressive, not the most talented. As a result, the cars that they built would be substandard, functional but with little style and prone to fall apart under close scrutiny.
Every car that came off the assembly line would receive a critique (politely referred to as "notes") from every executive in the company. Some of the critiques would suggest improvements to the car, others would suggest changes that would make it worse. Some would be contradictory ("I think it would work better with eight cylinders," and "I don't think a car like this needs more than four cylinders."), and some would make no sense ("I don't feel the 'carness' of this car - it's just not coming across. Maybe you need to reassess your attitude towards four wheel drive," or "More!").
Why would executives need to be so critical of the work of their employees? Secretly, they know that, without the men and women toiling on the auto assembly line, the executives would have no job, and they resent relying on people who's work they don't really understand.
Each producer would have a staff of 10 to 12 mechanics in addition to those who work the line. Their job would be to take parts off a finished car and replace them with parts the staff members like better. Cars would take five times longer to finish and cost ten times what they currently do. Not only that, but they would have pieces that stick out at odd angles and don't function they way they were originally designed to.
A secondary industry would arise catering to the needs of would-be auto workers. Hundreds of books would be available that took people through the theory of auto assembly, as well as discussing practical aspects of making a career in the industry. The books would cover more or less the same territory (starting with liberally borrowing from the auto assembly line theories of Aristotle). They would have titles like 30 Days to Becoming a Professional Auto Worker, Life on the Line: The Advanced Auto Assembly Line Worker's Handbook and Auto.
Auto assembly would be taught at universities, where it would be considered a bird course by mechanical engineering students. On any given weekend, you could find a conference for would-be auto assembly line workers featuring seminars with titles like "Advanced Creative Auto Assembly," "The Nuts and Bolts of Engine Placement" and "Breaking Into the Auto Assembly Shop...The Legal Way." They would, for the most part, be taught by people who no longer work in the industry, or never did.
With a small number of notable exceptions, those who work on the auto assembly line would be the worst paid members of the auto industry. Moreover, if a car was extremely popular, all the credit would go to the CEO of the company.
Perhaps it's just as well that working on an auto assembly line isn't like screenwriting.