The chassis number is on the frame tunnel under the back seat in the type 1 and 3. In the type 2, the chassis number is on the right engine cover plate in the engine compartment.
Beginning with the 1965 model year, a nine-digit serial number system was instituted. In this system, the first two numbers are the first two digits of the car's model number and the third digit stands for the car's model year-"5" stands for 1965, "8" stands for 1968, etc. A tenth digit was added when production passed one million.