Alternator keeps blowing

[arfawcett]

94 SHO 3.2L This is the third alternator I have put on this piecer. Each time I recharge the battery before starting. The first time I put in a new battery as well. Each Alternator has lasted no more than 2 days. I checked the wiring harness that goes from battery to starter to alternator and vehicle power system. I replaced all wiring. Also I added a ground wire directly to the alternator from the battery as well as a hot directly from the alternator to battery. The alternator is putting out 10.5 volts currently wich means rectifier diodes are probably blown except for maybe one or two. The voltage regulator is internal so this is also the third new one of those. I thought maybe adding a fuse between the alternator and the load might save it. 80 amp fuse wich should be about 67% of rated output still is good however the alternator is dead. field and ground inputs read good with key on not sure what happens with the car running and alternator connected wouldnt think that would do it unless overdriven which should be impossible. maybe a spike if field makes and brakes? only other possibilty i can think of would be if there is a intermittent short in the starter solenoid? all connections of high current are completely clean and new. starter is the original. another thing is the tach stops working intermittently and then not at all with the alternator dead. Is it one that runs off of the alternator noise or could it be part of the problem?

[MyTaurus8AChevy]

Hmmm.... I'm thinking a spike or a intermittent short. Both can be a bear to trace down. If you want I can go to the library tomorrow for you and see if I can dig up a wiring diagram. Maybe you missed something that isn't obvious in the wiring and it could help you trace it down. Let me know if you need it. Good luck, and try not to pull your hair out will your tracing down the problem with it

[shorod]

Welcome to the forum!

With the car not running, what is the battery voltage? If you disconnect the negative cable from the battery, what is the battery voltage?

With the car running and your multimeter set for AC volts, measure the voltage at the battery. Do you read any significant AC voltage?

When replacing the alternator, you are disconnecting the battery, right?

-Rod

[NScarpi]

Another thing to look at is if the Alternator has a good ground. The easiest way to eliminate this as a possibility is to run a wire from negitive of the battery to it. The other thing you can try is when the car is running, take your voltmeter and measure from neg. to the alternator case. It should be zero or very close to that, if you find that you can measure voltage there, then you know that your not getting a good ground.