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I should add that if you use the battery's negative terminal for your ground and measure a proper voltage at the alternator's output lug but the voltage at the battery is very low you needn't bother with the other wiring on the alternator, just follow the wiring from the alternator's lug to the battery.

You can also to a voltage drop test (negative test lead to the alt's lug and positive test lead to the battery's positive terminal), the reading should be very low, more than half a volt and you need to track the drop using the same methodology until you find the cause; You can do this test across just the fusible link to see if the fusible link is the culprit, but you have to pull the section it's mounted in out of the fuse box housing so I usually test the drop across the whole thing first.