For 1981and newer the serial number just under the glove box on the passengers side of the vehicle. The first two numbers (not letters) indicate the last two digits of the year of manufacture.

For carts older then 1981 lift the seat and look for the aluminum I - beam that is close to the battery on the drivers side.

If it has 2 brake petals it is 1975 - 1980

Harley Davidson Golf Cart Serial number information.

From 1963 through 1982 Harley Davidson positioned their serial number on a metal plate located above the driver's side rear tire on the rear frame cross brace. Some electric models will have the plate located behind the batteries.

Golf Cart Serial numbers for 
Club Car & Harley Davidson on this page.  
Use the links below for others. 
E-Z-GO          Yamaha