Your information about the Cadillac is a little off, Henry Ford, and Ford Motor Company did not sell the car company to General Motors, he was, however, involved in developing the original design, but never built the car, it was built by Henry Leland.
In 1902, before he succeeded in bring his Model T to market, Henry Ford was part of an automobile venture that failed. The major investors in this venture brought in an expert to sell the assets of this failed company, his name was Henry Leland.
Henry Ford continued in the car business, successfully launching his own company, Ford Motor Company in 1903.
"After two unsuccessful attempts to establish a company to manufacture automobiles, the Ford Motor Company was incorporated in 1903 with Henry Ford as vice-president and chief engineer."
It was Henry Leland, with the assistance of Henry Ford's major investors from his first failed attempt at car building, who developed the first Cadillac and brought it to market in 1903.
"Henry Leland introduced the $850 Cadillac at the 1903 New York auto show. Within a week, he'd taken 2286 orders. Cadillac built nearly 2500 cars that first year--a huge number at the time."
General Motors bought Cadillac from the venture capitalists, retaining Henry Leland as president of the company in 1909.
By the time General Motors bought Cadillac, Henry Ford was no longer involved with the car company that developed it. By 1909, Henry Ford was enjoying his own success with the Model T.
"Henry Ford realized his dream of producing an automobile that was reasonably priced, reliable, and efficient with the introduction of the Model T in 1908. This vehicle initiated a new era in personal transportation. It was easy to operate, maintain, and handle on rough roads, immediately becoming a huge success."
Actually, Henry Ford was never really involved in the production of the Cadillac itself. Ford was an early partner of William Murphy and Lemuel W. Bowen. Both Murphy and Bowen were bankers behind Ford but they became disenchanted with Ford because Ford seem interested in making only racing cars. They brought in Henry Leland as a consultant. Leland had just produced a new engine for the Oldsmobile. However, Oldsmobile rejected Leland's design and Leland was looking for other financial backers. Leland showed Murphy and Bowen his new engine and together they three men, without Ford, started a new company called Cadillac. The first Cadillac was completed in 1902. Ford Motor company was not incorporated until the next year, 1903. Eventually, both the Oldsmobile and Cadillac were merged with other car makers to form General Motors in 1908. Ford remained a separate company.