Join Date: Sep 2000
Location: Shrewsbury, MA, USA
Not unless one of the diodes is bad. there are six diodes in an alternator, anyone of which can fail and draw power from the battery when the car is off. Will kill the battery over a period of about a week.
If you have an ohm meter:
Disconnect the negative cable from the battery. and the field and relay connector on the top of the alternator (conector with blue and yellow wires)
All of these tests should indicate a high reading (infinite resistance) in one direction and low (towards 0 ohms) in the other. If not then one or more diodes is bad. These tests will show show good, shorted or open field winding, or a shorted diode, but WILL NOT show a failed open diode.
Place one lead on the ohm meter on the R terminal and the other on the positive post on the back of the alternator, then reverse the leads at the same terminals.
Place one lead on the ohm meter on the R terminal and the other to the case of the alternator, then reverse the leads at the same terminals.
If the readings don't indicate high in one direction and low in the other, you have to pull the alternator apart to figure out which of the 6 diodes is bad. you do that by performing the same test on each diode. put one lead of the ohmmeter on the center lead of the diode, and one on the case. then reverse the leads. when you get to the diode that doesn't indicate a high reading in one direction and low in the other you've found the shorted diode. Check them all while your there before assuming only one is bad.
Open field or shorted stator:
Connect an ohm meter to the "F" terminal and to the "GRD" stud on the back of the alternator, and note the reading on the lowest scale. Meter should read between 7 and 20 ohms.
1969 Indy Pace Car
350/300HP RPO Z11
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