Like Detroit automakers taking on the Japanese a generation ago, the seven American solar panel makers that filed a trade case on Wednesday against China might find that a legal victory, if it comes, may not translate into business success.In the 1970s and ‘80s, American car companies won a long series of trade cases to limit Japanese car imports. Japan’s automakers responded by moving assembly lines to the United States, creating many new blue-collar jobs. But they kept most of the high-paying design and engineering positions back in Japan. The new factories in the United States not only shielded Japanese auto companies against most further trade protectionism but helped them stay competitive when the yen soared against the dollar.   Meanwhile, American consumers had many new, affordable choices in cars — while Detroit continued to have trouble competing with its Japanese rivals. Don’t be surprised if Chinese solar companies try to pursue a similar path, which could benefit American consumers of solar power if it helps propel the technology beyond its current niche status.