The Fiat 55-66 DT Tractor, a product of Fiat's extensive heritage in agricultural machinery, represents a robust and versatile utility tractor. Belonging to the well-regarded '66' series, this model, likely produced in the 1980s and early 1990s, is characterized by its dual-traction (4-wheel drive) capability, enhancing performance across varied terrains and demanding applications in agriculture, horticulture, and light industry. Known for its straightforward mechanical design and inherent reliability, the 55-66 DT is powered by a durable, naturally aspirated direct-injection diesel engine, typically around 55 PTO horsepower, engineered for strong low-end torque essential for heavy-duty tasks. Its straightforward design and emphasis on practical functionality make it a dependable workhorse. This Service Repair Workshop Manual provides comprehensive instructions for the maintenance, diagnosis, and repair of the Fiat 55-66 DT Tractor. It covers all essential systems, including detailed procedures for the engine, transmission, hydraulic system, electrical circuits, braking, steering, cooling, and fuel systems. The manual includes guidance on routine maintenance, major component overhauls, component replacement, and troubleshooting common issues. With in-depth technical specifications and torque values, this resource is designed to assist owners, mechanics, and technicians in preserving the longevity, performance, and operational integrity of their Fiat 55-66 DT Tractor.