Oh good, something else Joe doesn't know anything about.
Joe, auto manufacturers have relied on outside sources for parts for decades. In some cases they may own part of the company that builds their parts, but not always.
Do you really think that in 1965 Ford build EVERY single piece of the Ford Mustang in house? They did not.
Actually, the reverse of what you believe is true, in the 80s auto manufactures started utilizing vertical integration which meant they started buying the companies that they were getting the various parts from .
In fact, having these companies and being able to sell them off is what kept Ford from having to take a bailout like GM and Chrysler did.