AO...Both since it's a unit. They have to function together to pass testing.

 

Thanks! ^^

 

OP has left the building...........

 

OP has left the building.................

 

Ok, this is great info guys. It did it again this morning. voltage jumped strait up aster starting and I shut the car off. Started right back up as normal. If its a short I guess I need to trace the alt wire. I guess I need to check the connections on the starter too.

Its a 1 month old new high output alt. btw. Oh I did check the 3 pin plug on the alt too> No corrosion, looks good.

Is it possible my battery could do this? Its so intermittent that I would think the battery would be bad all the time.

Thanks

 

S wire is the control wire (on the 4 wire connector on the top of the alternator that goes to the ECM).

The B wire is a direct connect to the battery through the starter (the terminal on on the back of the alternator under the rubber cap).

The problem, the voltage regulator is not clipping the field to prevent the alternator from over voltage'g out of the B terminal.

Again, alternator puts out AC, converted of to DC via the diodes, and voltage out of B (if not controlled through the voltage regulator), will ramp up the faster that the alternator spins. Uncontrolled, not uncommon for the voltage to get up in the 20 volt range out of the B terminal.

So your problem is in the voltage regulator, if this is a new problem that it only happening with that alternator (could be just a bad voltage regulator ground).

Contact points of the voltage regulator to the alternator when it bolted in place,


So these, and the matching points on the voltage regulator needed to be cleaned and dielectric greased before the voltage regulator is bolted back in.


https://www.corvetteforum.com/forums...nator-fix.html

If you drop in another alternator and still have the same problem, then the problem is with the (S) sensor wire/ecm instead. So before doing anything, have the alternator spun up bench tested. If the alternator has a problem itself, then it will have the voltage run away problem when spun up on the bench test as well.



To add, depending on how deep the rabbit hole (not just a voltage regulator problem), could be a wire shortage problem in the diode/rectifier section instead ( upper cap section removed first after desoldering/clipping the lugs, as show first in this video/part behind the Q-tips in the above photo).