keep blowing alternator fuses in a 96 v8

[jjahamilton]

anyone know what might be causing me to continually pop fuses? I bought a rebuilt alternator about two months ago and it had worked fine until a week ago when it started to pop the fuse at about 4500rpm. After taking it on a trip last week, it now blows the fuse at only 3000rpm. I swapped the voltage regulator out for my old one thinking that might be the problem but nothing changed. Any ideas? Everything in the car works as it always has. I'm lost here.

 

[SHOZ123]

The 30A fuse? I would guess the wire is shorting out.

 

[kit352]

i had the same problem when i got my car. its the 30 amp in the main fuse block right? my main wiring harness was trashed and that wire was shorting out. ran a new feild wire from the alt to the fuse block and no more issues. if i peeled back the wire loom directly above the front valve cover i could see the chaffed wires. i just puiggy backed the wire to the alt power wire to see if it would work and it did.

 

[jjahamilton]

Well, I put in a new alternator wire straight from the post to the fuse block. Still pops the fuse at 3000rpms. It's driveable but not practical as if you know these cars, they love to go past 3000 rpms. Any other suggestions?

 

[kit352]

did you splice it into the harness bypassing the old wire or did you do it in series with the old one?

 

[jjahamilton]

Completely replaced the wire. Am I supposed to add the new one to the old one? My main wiring harness looks good too. I'm still lost.

 

[SHOZ123]

The alternator or regulator must be bad. Have you done an ohm test to see if it's shorted?

 

[jjahamilton]

where would I touch to test? I have a meter so I'll do it but I need to know where to test.

 

[SHOZ123]

Take out the fuse and touch the side that is not hot (side going to the alternator) with one probe and the engine block with another while the meter is set on ohms.

Does the fuse blow right away?

 

[jjahamilton]

I will check the ohms when I get home, but the fuse blows as the tach passes 3000-3500. Same place for a while now. Like I said at first, it used to blow them at around 5000 rpms. I don't know why it would change. I'll check the ohm reading and let you know ASAP. Thank you guys for your help so far.

 

[SHOZ123]

Then if it is rpm related the alternator is definitely the suspect. Either the wire is somehow shorting out at certain speeds or the wire is good. Any short in the wire will blow the fuse as soon as power is supplied so using and ohm meter will show that the wire is good when the car is just sitting there.

 

[wymjym]

If the voltage regulator is 'going' out it would make sense that the solid state components are less (and less) able to deal with the output, possibly allowing a spike in voltage and a larger spike in amperage.
or it could be some weird wiring that is moving around at certain rpms (vibrations) and shorting it out.
wj

 

[jjahamilton]

No resistance according to the meter. The alternator has a clear path to the fuse block and nothing is shorting out according to the meter. I'm going with a possible solution, although expensive. I'm going to get another alternator (luckily, Kragen's here in town has one in stock) and I'll let you know what happens.

 

[jjahamilton]

Thank you SHOZ123. You saved my life. It was indeed the alternator. I would have gone on trying things forever, (trying to avoid buying a new alt.) but you told me what it was and how right you are. Thanks again.