When you connect up the ammeter, you are looking for a value of less than 100 ma. Hopefully, closer to 50ma. If it is more than this amount (200-300ma) then you must start pulling fuses to determine which circuit has the leak.

However, many times these situations can be traced back to the alternator. Disconnect all wires to the back of the alternator and see if the ammeter drops down to acceptable levels.