Hey guys i got an 88 firebird 5.0 TBI. I have replaced the alternator and the battery 4 times, and the battery will not hold a charge. Each time that Ive had Oreillys and Autozone test the alt. and the battery, the alt regulator always comes back as FAILED. Idk what to do anymore. Ive replaced the battery cables with brand new ones...no change. I cleaned all of the grounds and made sure that they were on bare metal... no change. Made sure all grounds and fuseable links to the starter were secure and clean. All of my fuses are good and the braided ground on the passenger side of the engine is good as well. Today I had a family friend look at the voltage reg pigtail. Mine has three wires: A thick red wire(which always has fire to it, idk if its supposed to), and thinner brown wire, and a black wire. The black and brown have no fire to them. When the black and the red were touched while the car was running, the idle came down and the battery showed to be charging. Once he let go the battery then went back to not being recharged. Idk guys im real down rn, with this car, I dont wanna junk/sell her over something like this but man like my confidence is in pieces, please help!

 

The brown wire should be a 12V switched and is the wire telling the alternator to charge. If that wire had no power to it while the engine is on the alternator will make no power, the pulley will just be spinning and cause the battery to drain. Find out if that wire has 12V + power with the engine on.

Also, is the alternator being tested on the vehicle? Is the parts store testing them before the part leaves the store when it's new?

 

Ohhh okay so that explains why when my friend touched the red wire to the brown wire, that thats why then it started to work. Would it be wise to splice those together? Would you suggest getting another alt? I had this one tested in and out of the vehicle. and this latest alt was tested before i took it home, and it had passed

 

You may have just blown the fuse on the brown wire. You could splice into the red wire but that is constant power and could drain your battery or shorten the life span of your alternator. Best long term solution is to fix the brown wire if that's the problem.

 

If you are using cheap AutoZone or O'Riley's alternators that's a big part of your problem. They are JUNK and you will keep replacing them till you buy a quality unit. Order a Powermaster from Summit, etc.

GD

 

Some NAPA stores will not even sell a reman alternator or starter. They have changed rebuilders so many times, that warranties are not honored. The latest place that is doing the rebuilds are only replacing the defective component(s). You are not getting a completely remanufactured piece with all new parts. As I understand it, there is 1 rebuilder that supplies all the parts stores.

 

On that connector there are letters molded into it. The S terminal is the heavy red and goes to a fusible link to the starter. This means it is hot all of the time. It is the alternator sense terminal for voltage regulation.

The other two terminals on that connector (the pigtail with the wires), are only hot with the ignition on. The F terminal being fed by the C-H/FAN fuse.

And the L terminal being fed by the GAGES fuse. A digital dash car has a small light bulb in series with that feed. A non-digi car has a resistor in series with that fuse.

The odd thing is, that a hot on either F or L will cause the alternator to charge. So not sure why GM wired it this way, but that is what the '88 FSM shows.

So check those two fuses first, if the C-H/FAN fuse is blown the engine coolant fan won't work either.

RBob.

 

Redundancy. Isolated fuse failure or bulb failure won't cripple the charging system.

Most alternators will self excite though if you get their RPM's way up. Like 5k rpm alt shaft speed. Not sure about CS alts but the SI ones will.

GD

 

But how would you know if the alternator failed? Wouldn't knowing that be better then using screwy setups?

RBob.

 

Well if the bulb fails and you have a digi-dash then you won't know if the alt fails. But the giveaway would be no battery warning light during key-on. The operator is supposed to check the operation of all warning lamps prior to driving. An inoperative warning lamp should definitely be noted in the log book. LoL.

If you have a gauge it should be independent of the alternator so failure would be obvious.

That's all just guessing.... But sure!

GD

 

The bulb on the digi-dash cars is hidden, not view-able.

RBob.

 

Some engineer needed to be fired over that.

GD

 

Hey guys I've changed the ignition switch and the brown wire on the alternator still has no power. Ive heard and now read that the C/H Fan fuse may have something to do with my problem? Cause idk who had this car before me, but the people removed the electric fan and installed a traditional "waterpump mounted" fan and removed the Fan fuse, sooooo idk what do you guys think? Could someone give me a schematic for the wires that go to and from the alternator. So if i replace the fuse, will the alternator finally charge?

 

It should start to charge, but this depends upon how hacked up the harness is.

RBob.

 

WOW. It even says on that wiring diagram, "Hidden Generator Lamp".

 

Well gentlemen a quick update. Ive bought another good alternator from Autozone, and took it to my dads friend today to have it put on. The mechanic bought a whole book about my car, and he's come to the conclusion that the C/H Fan Fuse is most likely the case of this whole damn problem. Judging by the schematic that RBob gave me, then that is the only reason, considering too that I dont have a digital dash. Plus the previous man to work on the charging harness had crossed the brown and black wires, like bruh. What do you guys think so far? Could this be the light at the end of the tunnel for me?

 

I can't take it anymore.
How many times and how many different ways must you be told that the alternator WILL NOT CHARGE without +12v on the brown wire?
And it does not matter what dash you have.
You need +12v on the brown wire for the alternator to charge. Period.

 

Damn someone is sour today haha. Keep in mind that I'm 21, so I'm not a "Senior Member" like you are. I am asking questions like we all do on here, for the general purpose of finding out the answer. So if you "can't take it anymore", then please don't comment then.

 

Only one way to know - either fix the brown wire circuit or run a switched 12v to the brown wire (F - field flash) wire and see if you get consistent charging. You can temp test this with a jumper wire from the batt lug on the alt to the F terminal. Just remove when not running or you will drain the battery.

GD