Test Lamp Method
With rectifier end shield and stator assembly separated from alternator proceed as follows: Test rectifiers (diodes) with a 12 volt battery and a test lamp, (No. 67 bulb, 4 candlepower) by connecting one side of test lamp to negative battery post and other side to positive battery post. Contact heat sink of rectifier with one test probe, and the other test probe to strap on top of rectifier. Now reverse probes, if lamp lights in one direction but does not light in other direction, rectifier is good. If lamp lights in both directions, rectifier is shorted. If lamp does not light in either direction, rectifier is open.