96 freightliner Detailed diagram of a truck engine?

It would help to know which motor you had. Detroit Diesel, Caterpillar, and Cummins motors were all available options during that model year. Which engine options specifically were available depends on exactly what model Freightliner you have. It could be either an 11.1 or 12.7 60 Series Detroit, it could be a 3206, 3306, or 3406E Caterpillar, it could be the L10, M11, or N14 Cummins, etc.