As I stated earlier, there is no point testing the system unless it is on and loaded. That means key on, engine running, preferably with the lights on. Test at idle and at fast idle.
At this point all you need to know is the total voltage drop in the system. Test the voltage between the alternator output stud and alternator case and note the reading. Then test the voltage at the battery posts, not the terminals. The difference between the two readings is the total voltage drop. Total voltage drop should be less than 1/2 volt.
If the reading is more than 1/2 volt, then you can test the positive side and the negative side separately to determine where the fault lies. To test the positive side put the positive meter lead on the alternator output stud and the negative lead on the positive battery post. To test the negative side put you negative meter lead on the alternator case and the positive lead on the battery negative post. The meter reading in each case will be the actual voltage drop in that part of the circuit. Easy.
Read that last bit as many times as it takes for you to understand it. A faulty test will give a faulty result. If you have any questions about the preceding just ask for clarification.
