Battery not charging (Page 1/2)
Cailibird FEB 28, 04:16 PM
Afternoon everyone. I have a 1988 4cyl 5spd fiero.

My battery is brand new and I replaced the alternator a few months ago. But my battery just keeps dying.

My battery tray is a little rusted but I used a wire brush to clean the grounds and where they sit. I do have a new one but idk if I'm supposed to weld them into where they are now? I don't have a welder

Anyways. I was wondering if that would be the issue or if something is wrong with my alternator? I'm not sure if I missed a wire on the alternator but could someone explain whats all connected to the alternator so I can be sure of that.

I put everything on back as the old one was. Only difference is that this new alternator had an additional post that wasn't on the old one. I can't remember if it was a negative or positive.

Any help is great help, I just don't want to have to sell this car for something more reliable.
Vintage-Nut FEB 28, 05:47 PM
EDIT - Start with a fully charged battery as the Generator/Alternator will not even try to charge an undercharged battery
Charge the battery
{Use a voltmeter to measure the battery after a day} 12.5 DC volts or better
If the battery won't hold 12.5 DC - replace it

Put the battery in the vehicle and start the engine
{Use a voltmeter to measure the battery at idle AND 3k RPM} 13.5 DC volts to 14.5 DC volts
If the Generator/Alternator won't charge the battery at 13.5 DC volts to 14.5 DC volts - check the belt first, then replace the Generator/Alternator

If the battery is good AND the Generator/Alternator is charging at 13-14 DC; then 'something' else is draining the battery called a "Parasitic Draw Issue"


quote
Only difference is that this new alternator had an additional post that wasn't on the old one


1988 Generator/Alternator has a big red wire at the stud/nut and a cable with three wires to connect



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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 02-28-2025).]

1985 Fiero GT FEB 28, 06:26 PM
Also, is the battery light lighting up in the gauge cluster when key on/engine off? If not, then that can be the issue, the alternator uses the resistance of the warning bulb to properly function, dead bulb, no charging.
Cailibird FEB 28, 06:37 PM

quote
Originally posted by 1985 Fiero GT:

Also, is the battery light lighting up in the gauge cluster when key on/engine off? If not, then that can be the issue, the alternator uses the resistance of the warning bulb to properly function, dead bulb, no charging.



It does turn on. But I also don't have the other two meters, the voltage meter and I don't remember the other one
1985 Fiero GT FEB 28, 06:47 PM

quote
Originally posted by Cailibird:


It does turn on. But I also don't have the other two meters, the voltage meter and I don't remember the other one



Ok, they shouldn't make a difference, well you know it's something more serious than a burnt out bulb haha.
Cailibird FEB 28, 07:26 PM

quote
Originally posted by 1985 Fiero GT:


Ok, they shouldn't make a difference, well you know it's something more serious than a burnt out bulb haha.



Well yeah I know. But the voltage meter kind of does in this situation, I've just seen people mention it in other posts.

I'm currently trying to get a new battery and then get home to do some testing. I will get back to you guys
olejoedad FEB 28, 07:33 PM
On the small plug on the alternator, with KEY ON...ENGINE NOT RUNNING

Orange wire - 12v
Red wire - 12v

With KEY OFF

Orange wire - no voltage
Red wire - 12v

Edited to correct mistake.
Thanks Vintage!

[This message has been edited by olejoedad (edited 03-01-2025).]

Vintage-Nut FEB 28, 10:43 PM
My PFSM says different...

To check the small plug with the three wires:
With the KEY OFF
*Only the S terminal {red wire to the battery} must measure 12V
*No Voltage on L terminal [brown} and F terminal {brown/white}

With the KEY RUN {Engine NOT Running}
S terminal {red wire to the battery} will still have 12V
*Check terminals L and F both have 12V
If no, check GAGES fuse on L, and FAN E fuse on F

[This message has been edited by Vintage-Nut (edited 02-28-2025).]

Patrick FEB 28, 11:42 PM

Temporarily disconnect the single wire that goes to each headlight motor and see if this makes a difference with your battery dying.
Dennis LaGrua MAR 01, 04:24 AM
Easy test, Start engine. Measure for voltage across battery terminals. If alternator is good, reading should be 13v-13.5V after just starting up

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "