I think it would shock most folks to know that most of their vehicle components are NOT made by the OEM. I have hauled assembly plant production parts for all the big three U.S. OEM's for a lot of years. The OEM's really only "make" stamped body parts. Even their engines, the vast majority of the components from valves to timing gears to flywheels, are made by 3rd parties. Absolutely NONE of the interior components are made by any OEM. The bulk of interior components from dashes to headliners to seats is made by Leer. Similar thing for wheels, brakes, axles, lights, etc, etc, etc. Accuride makes the largest percentage of wheels for production assembly plants. American Yazaki, thru a plant in Mexico, makes the lion's share of GM's wiring harnesses. I have even hauled glass produced at the Ford Glass Plant in Broken Arrow, OK to GM and Mopar assembly plants. That glass plant also produces a lot of glass used for windows in buildings! I think PPG took that plant over now. Just take the time if you can and watch the number of trucks that roll in and out of a Ford, GM, etc assembly plant. They are not there because it is a fun place to spend a few hours. Most plants are on a 15 min appointment window for each truck to arrive, to coincide with the assembly line timing, depending on which dock and component. Do not, I repeat, do not arrive more than 15 min early or later than 15 min late from you scheduled time our you will be in deep doo doo. And even with that in mind, there is usually a line of trucks at the gate waiting to check in. I am glad I don't mess with that stuff anymore. It is truly a logistics nightmare not for the faint of heart.
Any mess up that causes a assembly line to shut down costs over $100K per hour the line is down. The line has a two hour window before it will be out of a particular component. I have seen parts brought in by helicopter to keep the line up until the regular scheduled shipment can arrive.