This weekend, Hon Hai Precision Industry Co's Terry Gou finally had his moment of victory.

On Saturday, Gou and Sharp Corp. President Kozo Takahashi gathered in front of more than 300 reporters at the Osaka-based company's Sakai plant, flanked by the flags of Taiwan and Japan. They beamed and shook hands as they finalized a rescue plan for Hon Hai, also known as Foxconn, to take control of Sharp for ¥389 billion ($3.5 billion). It was a rare moment of peace for the hard-charging Gou, who spent four years chasing the Japanese electronics maker and overcame long odds and last-minute pitfalls to win.

Hon Hai's chairman won't have long to celebrate: The turnaround promises to be even harder than the takeover. With a sprawl of businesses making appliances, solar equipment and flat panels for mobile devices, Sharp is seeing its earnings deteriorate every quarter. Yet, as part of the rescue deal, Gou pledged to keep the company intact, respect its independence and try to preserve jobs. He will have a hard time keeping those agreements if he wants to reverse Sharp's fortunes and boost profits by getting more business from customers such as Apple Inc.