On Car Test

NOTE: OH vehicle testing is described as part of Overhaul procedure in this article.

Remove sensing diode block from the alternator before making tests. Check stator phases for ground to alternator frame, using a 110 volt test lamp. This is a delta-connected stator, therefore if one phase shows ground, all phases will be similarly affected.
Check continuity of each phase. All readings should be approximately the same (check with ohmmeter). Start engine and run at 460 RPM (1, 000 alternator RPM) and connect an A.C. voltmeter or 12 volt test lamp between two of the three A.C. terminals in turn. Voltage or lamp brilliancy should be the same across phases 1-2, 2-3, and 1-3. A pronounced difference in voltage reading or lamp brilliancy indicates shorted or ground stator terminals.