Voltage regulator failure modes

[montieth]

What are the failure modes of the voltage reguators? Is an intermittant failure to regulate voltage a typical behavior? Sitting idling its fine, rev, no issues. Then suddenly while idling again it will spike past 30 volts and settle back down again. Contacts on the regulator/connector have been cleaned and the wiring appears sound.

[rmel]

Here's a recent thread you may find of use.
viewtopic.php?f=14&t=11547&p=86395#p86395

I'd be more suspicious of an intermittent connection than a bad regulator.
The regulator is solid state and when they fail they typically give up the
ghost failing hard.

If the D+ terminal going to the regulator (and one side of the warning light) goes low,
e.g. and open or poor connection, the regulator will turn on driving the field winding DF
hard causing high output voltage. A bad connection could be internal to the alternator
or simply oxidation of the connections of the terminals of the alternator.

[4x4Pinz]

What we find when people are complaining about erratic charging is the wires on the back of the alternator. They say they have checked them but I have found a little too and small the last stand breaks. Of course the molex connector at the air shroud had always been suspect and both need to be looked at very close. Pull on the wires to insure that the wire is in good shape and not just held in place by the insulation.

[pcolette]

Good point on the alternator wiring. A new alternator wiring harness is available for about $23 and includes the inner half of the Molex connector.