Alternator going bad?

[Gremlinsteve]

Brand new
Just replaced it too

 

[olds307 and 403]

Your alternator is charging at 13.8 volts. I would look at the fusible link, mine blew and no charging. Also the bulb must be good in the idiot light or no charging as well. I also ran a 4 gauge battery cable to the main battery post on the alternator to the battery positive.

 

[pontiacgp]

The housing of the alternator needs to have a good ground before the alternator will charge properly. Sounds like the alternator may not be the problem if the new one didn't cure the problem you had.

 

[HAFROD]

Funny, my 87 GMC truck is doing the same thing. I replaced alternator with a high amp 12si . It charges fine till AC is on high. I'm thinking it might need the blower motor changed. It's drawing some mega amps to do that.

 

[Gremlinsteve]

Ok

Let's look at the disable link
It is going to be located where?

 

[565bbchevy]

So the alternators that you have bought at a store and taken back were they tested at the store and verified faulty?

 

[Gremlinsteve]

No
I planned on doing to today

But I'm checking things off as I get suggestions on things I have not looked at yet

Like the fusible link

 

[airboatgreg]

Could he not disconnect the battery with the car running, and if the engine dies the alternator is pooped?

Bad idea,
No

 

[airboatgreg]

Ok

13.8 ac off at stud on alt
12.2 with ac on

12.3 volts with plug unplugged from alt at idle ac on

12.3 volts measured at red wire on plug

12.2 volts at the positive terminal on battery at idle
Ac on or off

I know the alternator is regulating. It drops the engine rpm with it plugged in

I am irritable and it sounds to me like ya'all are going down the rabbit hole.
We have 13.8 on output so it's charging, rev to 2k rpm and see what you have. Check belt tension. I think you are fine

 

[Gremlinsteve]

This shows what it's doing at 1k rpm