Pretty sure Buck is right (as usual)
AC Spark Plug Division
In 1899, Albert Champion came to the U.S. as a champion bicycle racer. Albert found a job with the Stranhan brothers who had started Champion Spark plug Co in 1905 or 06 and began production in 1907. Albert was not happy in his job because he had no control over his work. He already had at least one spark plug patent from(1898) before leaving Europe. In 1908 he went to see Billy Durant. William C. Durant of the Buick Motor Co. Durant ask to see some of this proto types. Buick at that time was using Rajah spark plugs. Albert told Durant he would return with some the following day which he did. Durant thought they could mfg Albert's designs cheaper than buying the Rajah. He set Albert up in a workshop in Flint,MI. Albert went to work right away producing spark plugs to be used in the Buicks. Albert & Billy formed "Champion Ignition Co. Very shortly later the Stranahan Brothers ("Champion Spark Plug Co") Informed them they could not use the name "Champion" as they had it copyrighted. At that time the name was changed to AC (A)lbert (C)hampion. The company then became "AC Flint" This name was copyrighted in the later part of 1908. In 1927 AC Flint became a division or General Motors. (Found in William Durants papers after his death)
AC-Delco
In 1974, in an effort to streamline its operations and marketing, General Motors merged the AC Spark Plug with United Delco, which for years had been selling to the same customers, to create the new AC-Delco.