Complex sentence: Similar systems have been built under license by Lucas, Hitachi Automotive Products, Nippondenso, and other companies; though their key components look similar to L-Jetronic parts, those systems should not be called L-Jetronic and parts are usually not compatible.
Split into simpler sentences: Similar systems have been built under license by Lucas, Hitachi Automotive Products, Nippondenso. However, although their key components look similar to L-Jetronic parts, those systems should not be called L-Jetronic and parts are usually not compatible.